Data Science Interview Q&A | IDM Techpark Coimbatore

Data Science Interview Questions and Answers

Data Science is one of the most in-demand skills in top tech companies, including IDM TechPark. Mastering both statistical analysis, machine learning, data visualization, databases, and deployment strategies makes a Data Scientist a valuable asset in modern software development. To secure a Data Science role at IDM TechPark, candidates must be proficient in technologies like Python, R, SQL, machine learning frameworks, data visualization tools, and cloud services, as well as be ready to tackle both the Data Science Online Assessment and Technical Interview Round.
To help you succeed, we have compiled a list of the Top 100 Data Science Interview Questions along with their answers. Mastering these will give you a strong edge in cracking Data Science interviews at IDM TechPark.

1. Reverse a String

Question: Write a function to reverse a string without using built-in functions.
Answer:

def reverse_string(s): return s[::-1] # Example usage print(reverse_string("hello")) # Output: "olleh"
2. Find the Missing Number

Question: Given an array of n-1 integers from 1 to n, find the missing number.
Answer:

def find_missing_number(arr): n = len(arr) + 1 total_sum = n * (n + 1) // 2 return total_sum - sum(arr) # Example usage print(find_missing_number([1, 2, 4, 5, 6])) # Output: 3
3. Check for Palindrome

Question: Write a function to check if a string is a palindrome.
Answer:

def is_palindrome(s): return s == s[::-1] # Example usage print(is_palindrome("madam")) # Output: True
4. Find the Largest Element in an Array

Question: Write a function to find the largest element in an array.
Answer:

def find_largest(arr): return max(arr) # Example usage print(find_largest([3, 1, 4, 1, 5, 9])) # Output: 9
5. Fibonacci Sequence

Question: Write a function to generate the nth Fibonacci number.
Answer:

def fibonacci(n): a, b = 0, 1 for _ in range(n): a, b = b, a + b return a # Example usage print(fibonacci(7)) # Output: 13
6. Find the First Non-Repeating Character

Question: Given a string, find the first non-repeating character.
Answer:

def first_non_repeating_char(s): for char in s: if s.count(char) == 1: return char return None # Example usage print(first_non_repeating_char("swiss")) # Output: "w"
7. Count the Number of Vowels

Question: Write a function to count the number of vowels in a given string.
Answer:

def count_vowels(s): vowels = 'aeiou' return sum(1 for char in s if char in vowels) # Example usage print(count_vowels("hello")) # Output: 2
8. Find the Intersection of Two Arrays

Question: Write a function to find the intersection of two arrays.
Answer:

def intersection(arr1, arr2): return list(set(arr1) & set(arr2)) # Example usage print(intersection([1, 2, 2, 1], [2, 2])) # Output: [2]
9. Merge Sorted Arrays

Question: Merge two sorted arrays into one sorted array.
Answer:

def merge_sorted_arrays(arr1, arr2): return sorted(arr1 + arr2) # Example usage print(merge_sorted_arrays([1, 3, 5], [2, 4, 6])) # Output: [1, 2, 3, 4, 5, 6]
10. Find the Factorial of a Number

Question: Write a function to calculate the factorial of a number using recursion.
Answer:

def factorial(n): if n == 0: return 1 return n * factorial(n - 1) # Example usage print(factorial(5)) # Output: 120
11. Check if a Number is Prime

Question: Write a function to check if a number is prime.
Answer:

def is_prime(n): if n <= 1: return False for i in range(2, int(n**0.5) + 1): if n % i == 0: return False return True # Example usage print(is_prime(7)) # Output: True
12. Rotate an Array

Question: Rotate an array by k positions.
Answer:

def rotate_array(arr, k): return arr[-k % len(arr):] + arr[:-k % len(arr)] # Example usage print(rotate_array([1, 2, 3, 4, 5], 2)) # Output: [4, 5, 1, 2, 3]
13. Find Duplicate in an Array

Question: Write a function to find if there are any duplicates in an array.
Answer:

def has_duplicates(arr): return len(arr) != len(set(arr)) # Example usage print(has_duplicates([1, 2, 3, 4, 5])) # Output: False
14. Sum of Two Numbers

Question: Write a function to find if any two numbers in an array sum up to a target value.
Answer:

def two_sum(arr, target): seen = set() for num in arr: if target - num in seen: return True seen.add(num) return False # Example usage print(two_sum([1, 2, 3, 4], 7)) # Output: True
15. Count the Number of Words in a String

Question: Write a function to count the number of words in a string.
Answer:

def word_count(s): return len(s.split()) # Example usage print(word_count("Hello world!")) # Output: 2
16. Find the Longest Substring Without Repeating Characters

Question: Write a function to find the length of the longest substring without repeating characters.
Answer:

def longest_unique_substring(s): char_set = set() left = 0 max_len = 0 for right in range(len(s)): while s[right] in char_set: char_set.remove(s[left]) left += 1 char_set.add(s[right]) max_len = max(max_len, right - left + 1) return max_len # Example usage print(longest_unique_substring("abcabcbb")) # Output: 3
17. Binary Search

Question: Implement binary search in a sorted array.
Answer:

def binary_search(arr, target): left, right = 0, len(arr) - 1 while left <= right: mid = (left + right) // 2 if arr[mid] == target: return mid elif arr[mid] < target: left = mid + 1 else: right = mid - 1 return -1 # Example usage print(binary_search([1, 2, 3, 4, 5], 4)) # Output: 3
18. Count Inversions in an Array

Question: Write a function to count the number of inversions in an array (pair of elements where the first is greater than the second).
Answer:

def count_inversions(arr): def merge_count_split_inv(arr, temp_arr, left, right): if left == right: return 0 mid = (left + right) // 2 inv_count = merge_count_split_inv(arr, temp_arr, left, mid) inv_count += merge_count_split_inv(arr, temp_arr, mid + 1, right) inv_count += merge_and_count(arr, temp_arr, left, mid, right) return inv_count def merge_and_count(arr, temp_arr, left, mid, right): i = left # Starting index for left subarray j = mid + 1 # Starting index for right subarray k = left # Starting index to be sorted inv_count = 0 while i <= mid and j <= right: if arr[i] <= arr[j]: temp_arr[k] = arr[i] i += 1 else: temp_arr[k] = arr[j] inv_count += (mid-i + 1) j += 1 k += 1 while i <= mid: temp_arr[k] = arr[i] i += 1 k += 1 while j <= right: temp_arr[k] = arr[j] j += 1 k += 1 for i in range(left, right + 1): arr[i] = temp_arr[i] return inv_count temp_arr = [0] * len(arr) return merge_count_split_inv(arr, temp_arr, 0, len(arr) - 1) # Example usage print(count_inversions([1, 20, 6, 4, 5])) # Output: 5
19. Implement a Queue using Two Stacks

Question: Implement a queue using two stacks.
Answer:

class QueueUsingStacks: def init(self): self.stack1 = [] self.stack2 = [] def enqueue(self, item): self.stack1.append(item) def dequeue(self): if not self.stack2: while self.stack1: self.stack2.append(self.stack1.pop()) return self.stack2.pop() if self.stack2 else None q = QueueUsingStacks() q.enqueue(1) q.enqueue(2) print(q.dequeue()) # Output: 1
20. Implement a Stack using Queues

Question: Implement a stack using two queues.
Answer:

class StackUsingQueues: def init(self): self.queue1 = [] self.queue2 = [] def push(self, item): self.queue1.append(item) def pop(self): if len(self.queue1) == 0: return None while len(self.queue1) > 1: self.queue2.append(self.queue1.pop(0)) item = self.queue1.pop() self.queue1, self.queue2 = self.queue2, self.queue1 return item stack = StackUsingQueues() stack.push(1) stack.push(2) print(stack.pop()) # Output: 2
21. Find the Missing Number in an Array of Consecutive Numbers

Question: Write a function to find the missing number in a sequence of consecutive numbers.
Answer:

def find_missing(arr): total_sum = sum(range(arr[0], arr[-1] + 1)) return total_sum - sum(arr) # Example usage print(find_missing([1, 2, 4, 5, 6])) # Output: 3
22. Check if a String is an Anagram

Question: Write a function to check if two strings are anagrams.
Answer:

def is_anagram(s1, s2): return sorted(s1) == sorted(s2) # Example usage print(is_anagram("listen", "silent")) # Output: True
23. Longest Common Prefix

Question: Write a function to find the longest common prefix in an array of strings.
Answer:

def longest_common_prefix(strs): if not strs: return "" prefix = strs[0] for string in strs[1:]: while string[:len(prefix)] != prefix: prefix = prefix[:-1] if not prefix: return "" return prefix # Example usage print(longest_common_prefix(["flower", "flow", "flight"])) # Output: "fl"
24. Find the Kth Largest Element in an Array

Question: Find the Kth largest element in an unsorted array.
Answer:

import heapq def find_kth_largest(arr, k): return heapq.nlargest(k, arr)[-1] # Example usage print(find_kth_largest([3, 2, 1, 5, 6, 4], 2)) # Output: 5
25. Check if a String is a Valid Parenthesis Expression

Question: Write a function to check if a given string of parentheses is valid.
Answer:

def is_valid_parentheses(s): stack = [] mapping = {")": "(", "}": "{", "]": "["} for char in s: if char in mapping: top_element = stack.pop() if stack else '#' if mapping[char] != top_element: return False else: stack.append(char) return not stack # Example usage print(is_valid_parentheses("()[]{}")) # Output: True

1. Median of Two Sorted Arrays

Question: Find the median of two sorted arrays.
Answer:

def findMedianSortedArrays(nums1, nums2): nums = nums1 + nums2 nums.sort() n = len(nums) if n % 2 == 0: return (nums[n//2 - 1] + nums[n//2]) / 2 return nums[n//2] # Example usage print(findMedianSortedArrays([1, 3], [2])) # Output: 2.0

2. Longest Increasing Subsequence

Question: Given an integer array, find the length of the longest strictly increasing subsequence.
Answer:

def lengthOfLIS(nums): if not nums: return 0 dp = [1] * len(nums) for i in range(1, len(nums)): for j in range(i): if nums[i] > nums[j]: dp[i] = max(dp[i], dp[j] + 1) return max(dp) # Example usage print(lengthOfLIS([10, 9, 2, 5, 3, 7, 101, 18])) # Output: 4

3. Find the Kth Smallest Element in an Array

Question: Given an unsorted array, find the Kth smallest element.
Answer:

import heapq def findKthSmallest(nums, k): return heapq.nsmallest(k, nums)[-1] # Example usage print(findKthSmallest([3, 2, 1, 5, 6, 4], 2)) # Output: 2

4. Top K Frequent Elements

Question: Given a non-empty array of integers, return the k most frequent elements.
Answer:

from collections import Counter import heapq def topKFrequent(nums, k): count = Counter(nums) return [item[0] for item in heapq.nlargest(k, count.items(), key=lambda x: x[1])] # Example usage print(topKFrequent([1,1,1,2,2,3], 2)) # Output: [1, 2]

5. Word Break Problem

Question: Given a string and a dictionary of words, determine if the string can be segmented into a space-separated sequence of dictionary words.
Answer:

def wordBreak(s, wordDict): dp = [False] * (len(s) + 1) dp[0] = True for i in range(1, len(s) + 1): for word in wordDict: if i >= len(word) and dp[i - len(word)] and s[i - len(word):i] == word: dp[i] = True break return dp[len(s)] # Example usage print(wordBreak("leetcode", ["leet", "code"])) # Output: True

6. Serialize and Deserialize Binary Tree

Question: Design an algorithm to serialize and deserialize a binary tree.
Answer:

class TreeNode: def __init__(self, val=0, left=None, right=None): self.val = val self.left = left self.right = right class Codec: def serialize(self, root): def dfs(node): if not node: return "None" return str(node.val) + "," + dfs(node.left) + "," + dfs(node.right) return dfs(root) def deserialize(self, data): def dfs(): val = next(vals) if val == "None": return None node = TreeNode(int(val)) node.left = dfs() node.right = dfs() return node vals = iter(data.split(",")) return dfs() # Example usage codec = Codec() tree = TreeNode(1, TreeNode(2), TreeNode(3)) serialized = codec.serialize(tree) print(serialized) # Output: "1,2,None,None,3,None,None" deserialized = codec.deserialize(serialized)

7. Find All Anagrams in a String

Question: Given a string s and a non-empty string p, find all the start indices of p’s anagrams in s.
Answer:

from collections import Counter def findAnagrams(s, p): result = [] p_count = Counter(p) s_count = Counter(s[:len(p) - 1]) for i in range(len(p) - 1, len(s)): s_count[s[i]] += 1 if s_count == p_count: result.append(i - len(p) + 1) s_count[s[i - len(p) + 1]] -= 1 if s_count[s[i - len(p) + 1]] == 0: del s_count[s[i - len(p) + 1]] return result # Example usage print(findAnagrams("cbaebabacd", "abc")) # Output: [0, 6]

8. Find the Longest Palindromic Substring

Question: Given a string s, find the longest palindromic substring.
Answer:

def longestPalindrome(s): def expand_around_center(left, right): while left >= 0 and right < len(s) and s[left] == s[right]: left -= 1 right += 1 return s[left + 1:right] longest = "" for i in range(len(s)): odd = expand_around_center(i, i) even = expand_around_center(i, i + 1) longest = max(longest, odd, even, key=len) return longest # Example usage print(longestPalindrome("babad")) # Output: "bab" or "aba"

9. N-Queens Problem

Question: Solve the N-Queens puzzle, where you need to place N queens on an N×N chessboard such that no two queens threaten each other.
Answer:

def solveNQueens(n): def solve(board, row): if row == n: result.append(["".join(row) for row in board]) return for col in range(n): if col not in columns and row - col not in diag1 and row + col not in diag2: columns.add(col) diag1.add(row - col) diag2.add(row + col) board[row][col] = 'Q' solve(board, row + 1) columns.remove(col) diag1.remove(row - col) diag2.remove(row + col) board[row][col] = '.' result = [] columns, diag1, diag2 = set(), set(), set() board = [['.' for _ in range(n)] for _ in range(n)] solve(board, 0) return result # Example usage print(solveNQueens(4))

10. Word Ladder

Question: Given two words (beginWord and endWord), and a dictionary, find the length of the shortest transformation sequence from beginWord to endWord, such that only one letter can be changed at a time.
Answer:

from collections import deque def ladderLength(beginWord, endWord, wordList): wordList = set(wordList) if endWord not in wordList: return 0 queue = deque([(beginWord, 1)]) while queue: word, level = queue.popleft() if word == endWord: return level for i in range(len(word)): for c in 'abcdefghijklmnopqrstuvwxyz': next_word = word[:i] + c + word[i+1:] if next_word in wordList: wordList.remove(next_word) queue.append((next_word, level + 1)) return 0 # Example usage print(ladderLength("hit", "cog", ["hot", "dot", "dog", "lot", "log", "cog"])) # Output: 5

11. Longest Common Subsequence

Question: Given two strings, find the length of the longest common subsequence.
Answer:

def longestCommonSubsequence(text1, text2): m, n = len(text1), len(text2) dp = [[0] * (n + 1) for _ in range(m + 1)] for i in range(1, m + 1): for j in range(1, n + 1): if text1[i - 1] == text2[j - 1]: dp[i][j] = dp[i - 1][j - 1] + 1 else: dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]) return dp[m][n] # Example usage print(longestCommonSubsequence("abcde", "ace")) # Output: 3

12. Maximum Subarray Sum (Kadane's Algorithm)

Question: Given an integer array, find the contiguous subarray (containing at least one number) that has the largest sum.
Answer:

def maxSubArray(nums): max_sum = current_sum = nums[0] for num in nums[1:]: current_sum = max(num, current_sum + num) max_sum = max(max_sum, current_sum) return max_sum # Example usage print(maxSubArray([-2, 1, -3, 4, -1, 2, 1, -5, 4])) # Output: 6

13. Find Minimum Path Sum in a Grid

Question: Given a m x n grid filled with non-negative numbers, find a path from the top left to the bottom right, which minimizes the sum of the numbers along its path.
Answer:

def minPathSum(grid): m, n = len(grid), len(grid[0]) for i in range(1, m): grid[i][0] += grid[i-1][0] for j in range(1, n): grid[0][j] += grid[0][j-1] for i in range(1, m): for j in range(1, n): grid[i][j] += min(grid[i-1][j], grid[i][j-1]) return grid[-1][-1] # Example usage print(minPathSum([[1, 3, 1], [1, 5, 1], [4, 2, 1]])) # Output: 7

14. Minimum Window Substring

Question: Given two strings s and t, return the minimum window in s which will contain all the characters in t.
Answer:

from collections import Counter def minWindow(s, t): if not s or not t: return "" t_count = Counter(t) s_count = Counter() required = len(t_count) formed = 0 left, right = 0, 0 ans = float("inf"), None, None while right < len(s): char = s[right] s_count[char] += 1 if s_count[char] == t_count[char]: formed += 1 while left <= right and formed == required: char = s[left] if right - left + 1 < ans[0]: ans = right - left + 1, left, right s_count[char] -= 1 if s_count[char] < t_count[char]: formed -= 1 left += 1 right += 1 return "" if ans[0] == float("inf") else s[ans[1]:ans[2]+1] # Example usage print(minWindow("ADOBECODEBANC", "ABC")) # Output: "BANC"

15. Perfect Squares

Question: Given a positive integer n, return the least number of perfect square numbers that sum to n.
Answer:

def numSquares(n): dp = [float("inf")] * (n + 1) dp[0] = 0 for i in range(1, n + 1): j = 1 while j * j <= i: dp[i] = min(dp[i], dp[i - j * j] + 1) j += 1 return dp[n] # Example usage print(numSquares(12)) # Output: 3 (4 + 4 + 4)

16. Jump Game

Question: Given an array of non-negative integers, where each element represents your maximum jump length from that position, determine if you can reach the last index.
Answer:

def canJump(nums): last_pos = len(nums) - 1 for i in range(len(nums) - 2, -1, -1): if i + nums[i] >= last_pos: last_pos = i return last_pos == 0 # Example usage print(canJump([2,3,1,1,4])) # Output: True

17. Maximal Rectangle

Question: Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing only 1's and return its area.
Answer:

def maximalRectangle(matrix): if not matrix: return 0 n, m = len(matrix), len(matrix[0]) heights = [0] * m max_area = 0 for row in matrix: for i in range(m): heights[i] = heights[i] + 1 if row[i] == '1' else 0 max_area = max(max_area, largestRectangleArea(heights)) return max_area def largestRectangleArea(heights): stack = [-1] max_area = 0 for i, h in enumerate(heights + [0]): while heights[stack[-1]] > h: h_idx = stack.pop() height = heights[h_idx] width = i - stack[-1] - 1 max_area = max(max_area, height * width) stack.append(i) return max_area # Example usage print(maximalRectangle([["1", "0", "1", "0", "0"], ["1", "0", "1", "1", "1"], ["1", "1", "1", "1", "1"]])) # Output: 6

18. Clone Graph

Question: Given an undirected graph, clone it.
Answer:

class Node: def __init__(self, val=0, neighbors=None): self.val = val self.neighbors = neighbors if neighbors is not None else [] def cloneGraph(node): if not node: return None visited = {} def dfs(n): if n in visited: return visited[n] copy = Node(n.val) visited[n] = copy for neighbor in n.neighbors: copy.neighbors.append(dfs(neighbor)) return copy return dfs(node) # Example usage node1 = Node(1) node2 = Node(2) node3 = Node(3) node4 = Node(4) node1.neighbors = [node2, node4] node2.neighbors = [node1, node3] node3.neighbors = [node2, node4] node4.neighbors = [node1, node3] print(cloneGraph(node1)) # Output: A clone

of the graph.

19. Sliding Window Maximum:. Given an array nums, and an integer k, find the maximum sliding window.

`python from collections import deque def maxSlidingWindow(nums, k): result = [] dq = deque() for i, num in enumerate(nums): while dq and nums[dq[-1]] < num: dq.pop() dq.append(i) if dq[0] == i - k: dq.popleft() if i >= k - 1: result.append(nums[dq[0]]) return result # Example usage print(maxSlidingWindow([1,3,-1,-3,5,3,6,7], 3)) # Output: [3,3,5,5,6,7]

20. Combination Sum II

Question: Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sum to target.
Answer:

def combinationSum2(candidates, target): candidates.sort() result = [] def backtrack(start, target, path): if target == 0: result.append(path) return for i in range(start, len(candidates)): if i > start and candidates[i] == candidates[i - 1]: continue if candidates[i] > target: break backtrack(i + 1, target - candidates[i], path + [candidates[i]]) backtrack(0, target, []) return result # Example usage print(combinationSum2([10,1,2,7,6,5], 8)) # Output: [[1, 2, 5], [1, 7], [2, 6]]

21. Minimum Cost for Tickets

Question: You are given an array of days you are planning to travel and a list of ticket costs. Return the minimum cost of tickets.
Answer:

def mincostTickets(days, costs): dp = [0] * (max(days) + 1) day_set = set(days) for i in range(1, len(dp)): if i not in day_set: dp[i] = dp[i - 1] else: dp[i] = min(dp[i - 1] + costs[0], dp[max(0, i - 7)] + costs[1], dp[max(0, i - 30)] + costs[2]) return dp[-1] # Example usage print(mincostTickets([1,4,6,7,8,20], [2,7,15])) # Output: 11

22. Word Search

Question: Given a 2D board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring.
Answer:

def exist(board, word): def dfs(i, j, k): if not (0 <= i < len(board)) or not (0 <= j < len(board[0])) or board[i][j] != word[k]: return False if k == len(word) - 1: return True temp, board[i][j] = board[i][j], '/' result = dfs(i + 1, j, k + 1) or dfs(i - 1, j, k + 1) or dfs(i, j + 1, k + 1) or dfs(i, j - 1, k + 1) board[i][j] = temp return result for i in range(len(board)): for j in range(len(board[0])): if dfs(i, j, 0): return True return False # Example usage print(exist([["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], "ABCCED")) # Output: True

23. Number of Islands

Question: Given a 2D grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically.
Answer:

def numIslands(grid): if not grid: return 0 def dfs(i, j): if i < 0 or j < 0 or i >= len(grid) or j >= len(grid[0]) or grid[i][j] == '0': return grid[i][j] = '0' dfs(i + 1, j) dfs(i - 1, j) dfs(i, j + 1) dfs(i, j - 1) count = 0 for i in range(len(grid)): for j in range(len(grid[0])): if grid[i][j] == '1': count += 1 dfs(i, j) return count # Example usage print(numIslands([["1", "1", "1", "1", "0"], ["1", "1", "0", "1", "0"], ["1", "1", "0", "0", "0"], ["0", "0", "0", "0", "0"]])) # Output: 1

24. Basic Calculator II

Question: Implement a basic calculator to evaluate a simple expression string containing non-negative integers, '+', '-', '*', and '/' operators.
Answer:

def calculate(s): stack, num, sign = [], 0, '+' s = s + '+' for i, char in enumerate(s): if char.isdigit(): num = num * 10 + int(char) elif char in '+-*/' or i == len(s) - 1: if sign == '+': stack.append(num) elif sign == '-': stack.append(-num) elif sign == '*': stack[-1] = stack[-1] * num elif sign == '/': stack[-1] = int(stack[-1] / num) sign = char num = 0 return sum(stack) # Example usage print(calculate("3+2*2")) # Output: 7

25. Palindrome Partitioning

Question: Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s.
Answer:

def partition(s): def is_palindrome(sub): return sub == sub[::-1] def backtrack(start, path): if start == len(s): result.append(path[:]) return for end in range(start + 1, len(s) + 1): if is_palindrome(s[start:end]): path.append(s[start:end]) backtrack(end, path) path.pop() result = [] backtrack(0, []) return result # Example usage print(partition("aab")) # Output: [["a", "a", "b"], ["aa", "b"]]

1. Longest Substring Without Repeating Characters

Problem: Given a string, find the length of the longest substring without repeating characters.
Solution:

def lengthOfLongestSubstring(s): char_set = set() left = 0 max_len = 0 for right in range(len(s)): while s[right] in char_set: char_set.remove(s[left]) left += 1 char_set.add(s[right]) max_len = max(max_len, right - left + 1) return max_len # Example usage print(lengthOfLongestSubstring("abcabcbb")) # Output: 3

2. Valid Parentheses

Problem: Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
Solution:

def isValid(s): stack = [] mapping = {")": "(", "}": "{", "]": "["} for char in s: if char in mapping: top_element = stack.pop() if stack else '#' if mapping[char] != top_element: return False else: stack.append(char) return not stack # Example usage print(isValid("()[]{}")) # Output: True

3. Merge Intervals

Problem: Given a collection of intervals, merge any overlapping intervals.
Solution:

def merge(intervals): intervals.sort(key=lambda x: x[0]) merged = [] for interval in intervals: if not merged or merged[-1][1] < interval[0]: merged.append(interval) else: merged[-1][1] = max(merged[-1][1], interval[1]) return merged # Example usage print(merge([[1, 3], [2, 6], [8, 10], [15, 18]])) # Output: [[1, 6], [8, 10], [15, 18]]

4. Permutations

Problem: Given a collection of distinct integers, return all possible permutations.
Solution:

def permute(nums): result = [] def backtrack(path): if len(path) == len(nums): result.append(path[:]) return for num in nums: if num not in path: path.append(num) backtrack(path) path.pop() backtrack([]) return result # Example usage print(permute([1, 2, 3])) # Output: [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

5. Rotate Image

Problem: You are given an n x n 2D matrix representing an image. Rotate the image 90 degrees clockwise.
Solution:

def rotate(matrix): n = len(matrix) for i in range(n // 2): for j in range(i, n - i - 1): temp = matrix[i][j] matrix[i][j] = matrix[n - j - 1][i] matrix[n - j - 1][i] = matrix[n - i - 1][n - j - 1] matrix[n - i - 1][n - j - 1] = matrix[j][n - i - 1] matrix[j][n - i - 1] = temp # Example usage matrix = [ [1, 2, 3], [4, 5, 6], [7, 8, 9] ] rotate(matrix) print(matrix) # Output: [[7, 4, 1], [8, 5, 2], [9, 6, 3]]

6. Set Matrix Zeroes

Problem: Given an m x n matrix, if an element is 0, set its entire row and column to 0.
Solution:

def setZeroes(matrix): rows, cols = len(matrix), len(matrix[0]) row_zero = any(matrix[i][0] == 0 for i in range(rows)) col_zero = any(matrix[0][j] == 0 for j in range(cols)) for i in range(1, rows): for j in range(1, cols): if matrix[i][j] == 0: matrix[i][0] = matrix[0][j] = 0 for i in range(1, rows): for j in range(1, cols): if matrix[i][0] == 0 or matrix[0][j] == 0: matrix[i][j] = 0 if row_zero: for i in range(rows): matrix[i][0] = 0 if col_zero: for j in range(cols): matrix[0][j] = 0 # Example usage matrix = [ [1, 1, 1], [1, 0, 1], [1, 1, 1] ] setZeroes(matrix) print(matrix) # Output: [[1, 0, 1], [0, 0, 0], [1, 0, 1]]

7. Unique Paths

Problem: A robot is located at the top-left corner of a m x n grid. The robot can only move down or right. Find the number of unique paths to the bottom-right corner.
Solution:

def uniquePaths(m, n): dp = [[1] * n for _ in range(m)] for i in range(1, m): for j in range(1, n): dp[i][j] = dp[i - 1][j] + dp[i][j - 1] return dp[m - 1][n - 1] # Example usage print(uniquePaths(3, 7)) # Output: 28

8. Group Anagrams

Problem: Given an array of strings, group the anagrams together.
Solution:

from collections import defaultdict def groupAnagrams(strs): anagrams = defaultdict(list) for str_ in strs: anagrams[tuple(sorted(str_))].append(str_) return list(anagrams.values()) # Example usage print(groupAnagrams(["eat", "tea", "tan", "ate", "nat", "bat"])) # Output: [['eat', 'tea', 'ate'], ['tan', 'nat'], ['bat']]

9. Linked List Cycle

Problem: Given a linked list, determine if it has a cycle in it.
Solution:

class ListNode: def __init__(self, val=0, next=None): self.val = val self.next = next def hasCycle(head): slow, fast = head, head while fast and fast.next: slow = slow.next fast = fast.next.next if slow == fast: return True return False # Example usage # Creating a list with a cycle head = ListNode(3) head.next = ListNode(2) head.next.next = ListNode(0) head.next.next.next = ListNode(-4) head.next.next.next.next = head.next # Creating a cycle print(hasCycle(head)) # Output: True

10. Find Minimum in Rotated Sorted Array

Problem: Suppose an array of length n sorted in ascending order is rotated at some pivot. Find the minimum element.
Solution:

def findMin(nums): left, right = 0, len(nums) - 1 while left < right: mid = (left + right) // 2 if nums[mid] > nums[right]: left = mid + 1 else: right = mid return nums[left] # Example usage print(findMin([3, 4, 5, 1, 2])) # Output: 1

These problems cover a range of intermediate topics like dynamic programming, sorting, searching, backtracking, and more. Each solution includes an example to help you understand how to approach the problem and implement it. Let me know if you need any more problems or explanations!

11. Longest Palindromic Substring

Problem: Given a string, find the longest palindromic substring.
Solution:

def longestPalindrome(s):
def expand_around_center(left, right):
while left >= 0 and right < len(s) and s[left] == s[right]:
left -= 1
right += 1
return s[left + 1:right]

longest = ""
for i in range(len(s)):
odd = expand_around_center(i, i)
even = expand_around_center(i, i + 1)
longest = max(longest, odd, even, key=len)
return longest

# Example usage
print(longestPalindrome("babad")) # Output: "bab"

12. Find Duplicate in Array

Problem: Given an array of integers, find the duplicate number. The array has at least one duplicate, and the duplicate is within the range 1 to n (where n is the size of the array).
Solution:

def findDuplicate(nums):
slow, fast = nums[0], nums[0]
while True:
slow = nums[slow]
fast = nums[nums[fast]]
if slow == fast:
break

pointer1, pointer2 = nums[0], slow
while pointer1 != pointer2:
pointer1 = nums[pointer1]
pointer2 = nums[pointer2]
return pointer1

# Example usage
print(findDuplicate([1, 3, 4, 2, 2])) # Output: 2

Top K Frequent Elements

Problem: Given a non-empty array of integers, return the k most frequent elements.
Solution:

python

CopyEdit

14. Product of Array Except Self

Problem: Given an array nums, return an array such that each element at index i is the product of all the numbers in the array except nums[i].
Solution:

python

CopyEdit

def productExceptSelf(nums): result = [1] * len(nums) left, right = 1, 1 for i in range(len(nums)): result[i] *= left left *= nums[i] result[-i-1] *= right right *= nums[-i-1] return result # Example usage print(productExceptSelf([1, 2, 3, 4])) # Output: [24, 12, 8, 6]

15. Word Break

Problem: Given a string s and a list of words wordDict, determine if s can be segmented into a space-separated sequence of one or more dictionary words.
Solution:

python

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def wordBreak(s, wordDict): dp = [False] * (len(s) + 1) dp[0] = True for i in range(1, len(s) + 1): for word in wordDict: if i >= len(word) and s[i-len(word):i] == word: dp[i] = dp[i] or dp[i-len(word)] return dp[len(s)] # Example usage print(wordBreak("leetcode", ["leet", "code"])) # Output: True

16. Valid Sudoku

Problem: Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the rules.
Solution:

python

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def isValidSudoku(board): rows, cols, boxes = {}, {}, {} for i in range(9): for j in range(9): if board[i][j] != '.': if (i, board[i][j]) in rows or (j, board[i][j]) in cols or (i//3, j//3, board[i][j]) in boxes: return False rows[(i, board[i][j])] = True cols[(j, board[i][j])] = True boxes[(i//3, j//3, board[i][j])] = True return True # Example usage board = [ ["5","3",".",".","7",".",".",".","."], ["6",".",".","1","9","5",".",".","."], [".","9","8",".",".",".",".","6","."], ["8",".",".",".","6",".",".",".","3"], ["4",".",".","8",".","3",".",".","1"], ["7",".",".",".","2",".",".",".","6"], [".","6",".",".",".",".","2","8","."], [".",".",".","4","1","9",".",".","5"], [".",".",".",".","8",".",".","7","9"] ] print(isValidSudoku(board)) # Output: True

17. String to Integer (atoi)

Problem: Implement the atoi function, which converts a string to an integer.
Solution:

python

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def myAtoi(s): s = s.strip() if not s: return 0 sign = 1 if s[0] == '-': sign = -1 s = s[1:] elif s[0] == '+': s = s[1:] result = 0 for char in s: if not char.isdigit(): break result = result * 10 + int(char) result *= sign return max(min(result, 2**31 - 1), -2**31) # Example usage print(myAtoi("42")) # Output: 42

18. Substring with Concatenation of All Words

Problem: Given a string s and a list of words words, find all starting indices of substring(s) in s that is a concatenation of each word in words exactly once.
Solution:

python

CopyEdit

def findSubstring(s, words): word_len, word_count = len(words[0]), len(words) word_dict = {} for word in words: word_dict[word] = word_dict.get(word, 0) + 1 result = [] for i in range(word_len): left, right = i, i window = {} while right + word_len <= len(s): word = s[right:right + word_len] right += word_len if word in word_dict: window[word] = window.get(word, 0) + 1 while window[word] > word_dict[word]: window[s[left:left + word_len]] -= 1 left += word_len if right - left == word_len * word_count: result.append(left) else: window.clear() left = right return result # Example usage print(findSubstring("barfoothefoobarman", ["foo","bar"])) # Output: [0, 9]

19. Find Peak Element

Problem: A peak element is an element that is greater than its neighbors. Given an array, find a peak element.
Solution:

python

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def findPeakElement(nums): left, right = 0, len(nums) - 1 while left < right: mid = (left + right) // 2 if nums[mid] > nums[mid + 1]: right = mid else: left = mid + 1 return left # Example usage print(findPeakElement([1,2,3,1])) # Output: 2 (index of peak element 3)

20. Jump Game II

Problem: Given an array of non-negative integers representing the maximum jump length at each position, find the minimum number of jumps to reach the last index.
Solution:

python

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def jump(nums): jumps, current_end, farthest = 0, 0, 0 for i in range(len(nums) - 1): farthest = max(farthest, i + nums[i]) if i == current_end: jumps += 1 current_end = farthest return jumps # Example usage print(jump([2,3,1,1,4])) # Output: 2

21. Spiral Matrix

Problem: Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.
Solution:

python

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def spiralOrder(matrix): result = [] while matrix: result += matrix.pop(0) if matrix and matrix[0]: for row in matrix: result.append(row.pop()) if matrix: result += matrix.pop()[::-1] if matrix and matrix[0]: for row in matrix[::-1]: result.append(row.pop(0)) return result # Example usage print(spiralOrder([[1,2,3],[4,5,6],[7,8,9]])) # Output: [1, 2, 3, 6, 9, 8, 7, 4, 5]

22. Container with Most Water

Problem: Given an array of non-negative integers, find the two lines that together with the x-axis form a container, such that the container contains the most water.
Solution:

python

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def maxArea(height): left, right = 0, len(height) - 1 max_area = 0 while left < right: width = right - left area = min(height[left], height[right]) * width max_area = max(max_area, area) if height[left] < height[right]: left += 1 else: right -= 1 return max_area # Example usage print(maxArea([1,8,6,2,5,4,8,3,7])) # Output: 49

23. Decode Ways

Problem: A message containing letters from A-Z can be encoded as a number from 1 to 26. Given a string s containing only digits, return the total number of ways to decode it.
Solution:

python

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def numDecodings(s): if not s: return 0 dp = [0] * (len(s) + 1) dp[0] = 1 dp[1] = 1 if s[0] != '0' else 0 for i in range(2, len(s) + 1): if s[i - 1] != '0': dp[i] += dp[i - 1] if '10' <= s[i - 2:i] <= '26': dp[i] += dp[i - 2] return dp[len(s)] # Example usage print(numDecodings("12")) # Output: 2

24. Letter Combinations of a Phone Number

Problem: Given a string containing digits from 2-9, return all possible letter combinations that the number could represent.
Solution:

python

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def letterCombinations(digits): if not digits: return [] mapping = {'2': 'abc', '3': 'def', '4': 'ghi', '5': 'jkl', '6': 'mno', '7': 'pqrs', '8': 'tuv', '9': 'wxyz'} result = [''] for digit in digits: result = [prefix + char for prefix in result for char in mapping[digit]] return result # Example usage print(letterCombinations("23")) # Output: ['ad', 'ae', 'af', 'bd', 'be', 'bf', 'cd', 'ce', 'cf']

25. Balanced Binary Tree

Problem: Given a binary tree, determine if it is height-balanced.
Solution:

python

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class TreeNode: def __init__(self, val=0, left=None, right=None): self.val = val self.left = left self.right = right def isBalanced(root): def height(node): if not node: return 0 left = height(node.left) right = height(node.right) if left == -1 or right == -1 or abs(left - right) > 1: return -1 return max(left, right) + 1 return height(root) != -1 # Example usage root = TreeNode(1) root.left = TreeNode(2) root.right = TreeNode(2) root.left.left = TreeNode(3) root.left.right = TreeNode(3) root.left.left.left = TreeNode(4) print(isBalanced(root)) # Output: False

1. Reverse a String

Problem: Write a function to reverse a string.
Solution:

def reverseString(s): return s[::-1]

Example:
reverseString("hello") # Output: "olleh"

2. Find the Missing Number

Problem: Given an array of integers from 1 to n with one number missing, find the missing number.
Solution:

def findMissingNumber(nums): n = len(nums) + 1 total_sum = n * (n + 1) // 2 return total_sum - sum(nums)

Example:
findMissingNumber([1, 2, 4, 6, 3, 7, 8]) # Output: 5

3. Check for Anagram

Problem: Given two strings, write a function to check if they are anagrams of each other.
Solution:

def isAnagram(str1, str2): return sorted(str1) == sorted(str2)

Example:
isAnagram("listen", "silent") # Output: True

4. Find the Largest Element in Array

Problem: Write a function to find the largest element in an array.
Solution:

def findLargest(nums): return max(nums)

Example:
findLargest([1, 3, 2, 5, 4]) # Output: 5

5. Check Palindrome

Problem: Given a string, write a function to check if it is a palindrome.
Solution:

def isPalindrome(s): return s == s[::-1]

Example:
isPalindrome("racecar") # Output: True

6. Count Vowels in String

Problem: Write a function to count the number of vowels in a string.
Solution:

def countVowels(s): vowels = "aeiou" return sum(1 for char in s if char in vowels)

Example:
countVowels("hello") # Output: 2

7. Find the Factorial of a Number

Problem: Write a function to find the factorial of a number.
Solution:

def factorial(n): if n == 0 or n == 1: return 1 return n * factorial(n - 1)

Example:
factorial(5) # Output: 120

8. Fibonacci Sequence

Problem: Write a function to print the Fibonacci sequence up to a given number.
Solution:

def fibonacci(n): a, b = 0, 1 while a < n: print(a, end=" ") a, b = b, a + b

Example:
fibonacci(10) # Output: 0 1 1 2 3 5 8

9. Find the GCD of Two Numbers

Problem: Write a function to find the Greatest Common Divisor (GCD) of two numbers.
Solution:

def gcd(a, b): while b: a, b = b, a % b return a

Example:
gcd(48, 18) # Output: 6

10. Sum of Array Elements

Problem: Write a function to find the sum of elements in an array.
Solution:

def sumArray(arr): return sum(arr)

Example:
sumArray([1, 2, 3, 4]) # Output: 10

11. Find the Longest Palindromic Substring

Problem: Given a string, find the longest palindromic substring.
Solution:

Example:
longestPalindrome("babad") # Output: "bab"

12. Reverse an Integer

Problem: Write a function to reverse an integer.
Solution:

def reverseInteger(n): reversed_num = 0 while n != 0: reversed_num = reversed_num * 10 + n % 10 n = n // 10 return reversed_num

Example:
reverseInteger(123) # Output: 321

13. Find Prime Numbers in Range

Problem: Write a function to find all prime numbers in a given range.
Solution:

def is_prime(n): if n <= 1: return False for i in range(2, int(n**0.5) + 1): if n % i == 0: return False return True def primes_in_range(start, end): return [num for num in range(start, end + 1) if is_prime(num)]

Example:
primes_in_range(10, 30) # Output: [11, 13, 17, 19, 23, 29]

14. Check for Balanced Parentheses

Problem: Write a function to check if parentheses in a string are balanced.
Solution:

def isBalanced(s): stack = [] for char in s: if char in "({[": stack.append(char) elif char in ")}]": if not stack: return False top = stack.pop() if (top == '(' and char != ')') or (top == '{' and char != '}') or (top == '[' and char != ']'): return False return not stack

Example:
isBalanced("{[()]}") # Output: True

15. Find the Intersection of Two Arrays

Problem: Write a function to find the intersection of two arrays.
Solution:

def intersection(nums1, nums2): return list(set(nums1) & set(nums2))

Example:
intersection([1, 2, 2, 1], [2, 2]) # Output: [2]

16. Find Duplicate in Array

Problem: Write a function to find the duplicate number in an array of n + 1 integers.
Solution:

def findDuplicate(nums): slow, fast = nums[0], nums[0] while True: slow = nums[slow] fast = nums[nums[fast]] if slow == fast: break pointer1, pointer2 = nums[0], slow while pointer1 != pointer2: pointer1 = nums[pointer1] pointer2 = nums[pointer2] return pointer1

Example:
findDuplicate([1, 3, 4, 2, 2]) # Output: 2

17. Merge Two Sorted Arrays

Problem: Write a function to merge two sorted arrays into a sorted array.
Solution:

def mergeSortedArrays(arr1, arr2): result = [] i, j = 0, 0 while i < len(arr1) and j < len(arr2): if arr1[i] < arr2[j]: result.append(arr1[i]) i += 1 else: result.append(arr2[j]) j += 1 result.extend(arr1[i:]) result.extend(arr2[j:]) return result

Example:
mergeSortedArrays([1, 3, 5], [2, 4, 6]) # Output: [1, 2, 3, 4, 5, 6]

18. Rotate Array

Problem: Write a function to rotate an array by k steps.
Solution:

def rotateArray(arr, k): k = k % len(arr) # To handle k greater than array length return arr[-k:] + arr[:-k]

Example:
rotateArray([1, 2, 3, 4, 5], 2) # Output: [4, 5, 1, 2, 3]

19. Find All Subsets of a Set

Problem: Write a function to find all subsets of a set.
Solution:

def subsets(nums): result = [[]] for num in nums: result += [curr + [num] for curr in result] return result

Example:
subsets([1, 2]) # Output: [[], [1], [2], [1, 2]]

20. Find Kth Largest Element

Problem: Write a function to find the kth largest element in an array.
Solution:

import heapq def kthLargest(nums, k): return heapq.nlargest(k, nums)[-1]

Example:
kthLargest([3, 2, 1, 5, 6, 4], 2) # Output: 5

21. Find Peak Element

Problem: Write a function to find a peak element in an array.
Solution:

def findPeakElement(nums): left, right = 0, len(nums) - 1 while left < right: mid = (left + right) // 2 if nums[mid] > nums[mid + 1]: right = mid else: left = mid + 1 return left

Example:
findPeakElement([1, 2, 3, 1]) # Output: 2

22. Max Subarray Sum

Problem: Write a function to find the maximum sum of a contiguous subarray.
Solution:

def maxSubArray(nums): max_sum = current_sum = nums[0] for num in nums[1:]: current_sum = max(num, current_sum + num) max_sum = max(max_sum, current_sum) return max_sum

Example:
maxSubArray([-2, 1, -3, 4, -1, 2, 1, -5, 4]) # Output: 6

23. Find Missing Positive Integer

Problem: Write a function to find the smallest missing positive integer in an unsorted array.
Solution:

def firstMissingPositive(nums): nums = set(nums) i = 1 while i in nums: i += 1 return i

Example:
firstMissingPositive([1, 2, 0]) # Output: 3

24. Implement Trie (Prefix Tree)

Problem: Write a function to implement a trie data structure.
Solution:

class Trie: def __init__(self): self.children = {} self.end_of_word = False def insert(self, word): node = self for char in word: if char not in node.children: node.children[char] = Trie() node = node.children[char] node.end_of_word = True def search(self, word): node = self for char in word: if char not in node.children: return False node = node.children[char] return node.end_of_word

Example:
trie = Trie()
trie.insert("apple")
trie.search("apple") # Output: True

25. Merge Intervals

Problem: Write a function to merge overlapping intervals.
Solution:

def mergeIntervals(intervals): intervals.sort(key=lambda x: x[0]) result = [] for interval in intervals: if not result or result[-1][1] < interval[0]: result.append(interval) else: result[-1][1] = max(result[-1][1], interval[1]) return result

Example:
mergeIntervals([[1, 3], [2, 6], [8, 10], [15, 18]]) # Output: [[1, 6], [8, 10], [15, 18]]

I hope this is the format you're looking for! Let me know if you need further assistance.

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Data Science Interview Questions and Answers

Top 100 Data Science Interview Questions for Freshers

​1. Reverse a String

Question: Write a function to reverse a string without using built-in functions.

Answer:

def reverse_string(s): return s[::-1] # Example usage print(reverse_string("hello")) # Output: "olleh" 2. Find the Missing Number

Question: Given an array of n-1 integers from 1 to n, find the missing number.

Answer:

def find_missing_number(arr): n = len(arr) + 1 total_sum = n * (n + 1) // 2 return total_sum - sum(arr) # Example usage print(find_missing_number([1, 2, 4, 5, 6])) # Output: 3 3. Check for Palindrome

Question: Write a function to check if a string is a palindrome.

Answer:

def is_palindrome(s): return s == s[::-1] # Example usage print(is_palindrome("madam")) # Output: True 4. Find the Largest Element in an Array

Question: Write a function to find the largest element in an array.

Answer:

def find_largest(arr): return max(arr) # Example usage print(find_largest([3, 1, 4, 1, 5, 9])) # Output: 9 5. Fibonacci Sequence

Question: Write a function to generate the nth Fibonacci number.

Answer:

def fibonacci(n): a, b = 0, 1 for _ in range(n): a, b = b, a + b return a # Example usage print(fibonacci(7)) # Output: 13 6. Find the First Non-Repeating Character

Question: Given a string, find the first non-repeating character.

Answer:

def first_non_repeating_char(s): for char in s: if s.count(char) == 1: return char return None # Example usage print(first_non_repeating_char("swiss")) # Output: "w" 7. Count the Number of Vowels

Question: Write a function to count the number of vowels in a given string.

Answer:

def count_vowels(s): vowels = 'aeiou' return sum(1 for char in s if char in vowels) # Example usage print(count_vowels("hello")) # Output: 2 8. Find the Intersection of Two Arrays

Question: Write a function to find the intersection of two arrays.

Answer:

def intersection(arr1, arr2): return list(set(arr1) & set(arr2)) # Example usage print(intersection([1, 2, 2, 1], [2, 2])) # Output: [2] 9. Merge Sorted Arrays

Question: Merge two sorted arrays into one sorted array.

Answer:

def merge_sorted_arrays(arr1, arr2): return sorted(arr1 + arr2) # Example usage print(merge_sorted_arrays([1, 3, 5], [2, 4, 6])) # Output: [1, 2, 3, 4, 5, 6] 10. Find the Factorial of a Number

Question: Write a function to calculate the factorial of a number using recursion.

Answer:

def factorial(n): if n == 0: return 1 return n * factorial(n - 1) # Example usage print(factorial(5)) # Output: 120 11. Check if a Number is Prime

Question: Write a function to check if a number is prime.

Answer:

def is_prime(n): if n <= 1: return False for i in range(2, int(n**0.5) + 1): if n % i == 0: return False return True # Example usage print(is_prime(7)) # Output: True 12. Rotate an Array

Question: Rotate an array by k positions.

Answer:

def rotate_array(arr, k): return arr[-k % len(arr):] + arr[:-k % len(arr)] # Example usage print(rotate_array([1, 2, 3, 4, 5], 2)) # Output: [4, 5, 1, 2, 3] 13. Find Duplicate in an Array

Question: Write a function to find if there are any duplicates in an array.

Answer:

def has_duplicates(arr): return len(arr) != len(set(arr)) # Example usage print(has_duplicates([1, 2, 3, 4, 5])) # Output: False 14. Sum of Two Numbers

Question: Write a function to find if any two numbers in an array sum up to a target value.

Answer:

def two_sum(arr, target): seen = set() for num in arr: if target - num in seen: return True seen.add(num) return False # Example usage print(two_sum([1, 2, 3, 4], 7)) # Output: True 15. Count the Number of Words in a String

Question: Write a function to count the number of words in a string.

Answer:

def word_count(s): return len(s.split()) # Example usage print(word_count("Hello world!")) # Output: 2 16. Find the Longest Substring Without Repeating Characters

Question: Write a function to find the length of the longest substring without repeating characters.

Answer:

Question: Implement binary search in a sorted array.

Answer:

Question: Write a function to count the number of inversions in an array (pair of elements where the first is greater than the second).

Answer:

Question: Implement a queue using two stacks.

Answer:

Question: Implement a stack using two queues.

Answer:

Question: Write a function to find the missing number in a sequence of consecutive numbers.

Answer:

def find_missing(arr): total_sum = sum(range(arr[0], arr[-1] + 1)) return total_sum - sum(arr) # Example usage print(find_missing([1, 2, 4, 5, 6])) # Output: 3 22. Check if a String is an Anagram

Question: Write a function to check if two strings are anagrams.

Answer:

def is_anagram(s1, s2): return sorted(s1) == sorted(s2) # Example usage print(is_anagram("listen", "silent")) # Output: True 23. Longest Common Prefix

Question: Write a function to find the longest common prefix in an array of strings.

Answer:

Question: Find the Kth largest element in an unsorted array.

Answer:

import heapq def find_kth_largest(arr, k): return heapq.nlargest(k, arr)[-1] # Example usage print(find_kth_largest([3, 2, 1, 5, 6, 4], 2)) # Output: 5 25. Check if a String is a Valid Parenthesis Expression

Question: Write a function to check if a given string of parentheses is valid.

Answer:

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1. Reverse a String

def reverse_string(s): return s[::-1] # Example usage print(reverse_string("hello")) # Output: "olleh"
2. Find the Missing Number

def find_missing_number(arr): n = len(arr) + 1 total_sum = n * (n + 1) // 2 return total_sum - sum(arr) # Example usage print(find_missing_number([1, 2, 4, 5, 6])) # Output: 3
3. Check for Palindrome

def is_palindrome(s): return s == s[::-1] # Example usage print(is_palindrome("madam")) # Output: True
4. Find the Largest Element in an Array

def find_largest(arr): return max(arr) # Example usage print(find_largest([3, 1, 4, 1, 5, 9])) # Output: 9
5. Fibonacci Sequence

def fibonacci(n): a, b = 0, 1 for _ in range(n): a, b = b, a + b return a # Example usage print(fibonacci(7)) # Output: 13
6. Find the First Non-Repeating Character

def first_non_repeating_char(s): for char in s: if s.count(char) == 1: return char return None # Example usage print(first_non_repeating_char("swiss")) # Output: "w"
7. Count the Number of Vowels

def count_vowels(s): vowels = 'aeiou' return sum(1 for char in s if char in vowels) # Example usage print(count_vowels("hello")) # Output: 2
8. Find the Intersection of Two Arrays

def intersection(arr1, arr2): return list(set(arr1) & set(arr2)) # Example usage print(intersection([1, 2, 2, 1], [2, 2])) # Output: [2]
9. Merge Sorted Arrays

def merge_sorted_arrays(arr1, arr2): return sorted(arr1 + arr2) # Example usage print(merge_sorted_arrays([1, 3, 5], [2, 4, 6])) # Output: [1, 2, 3, 4, 5, 6]
10. Find the Factorial of a Number

def factorial(n): if n == 0: return 1 return n * factorial(n - 1) # Example usage print(factorial(5)) # Output: 120
11. Check if a Number is Prime

def is_prime(n): if n <= 1: return False for i in range(2, int(n**0.5) + 1): if n % i == 0: return False return True # Example usage print(is_prime(7)) # Output: True
12. Rotate an Array

def rotate_array(arr, k): return arr[-k % len(arr):] + arr[:-k % len(arr)] # Example usage print(rotate_array([1, 2, 3, 4, 5], 2)) # Output: [4, 5, 1, 2, 3]
13. Find Duplicate in an Array

def has_duplicates(arr): return len(arr) != len(set(arr)) # Example usage print(has_duplicates([1, 2, 3, 4, 5])) # Output: False
14. Sum of Two Numbers

def two_sum(arr, target): seen = set() for num in arr: if target - num in seen: return True seen.add(num) return False # Example usage print(two_sum([1, 2, 3, 4], 7)) # Output: True
15. Count the Number of Words in a String

def word_count(s): return len(s.split()) # Example usage print(word_count("Hello world!")) # Output: 2
16. Find the Longest Substring Without Repeating Characters

def find_missing(arr): total_sum = sum(range(arr[0], arr[-1] + 1)) return total_sum - sum(arr) # Example usage print(find_missing([1, 2, 4, 5, 6])) # Output: 3
22. Check if a String is an Anagram

def is_anagram(s1, s2): return sorted(s1) == sorted(s2) # Example usage print(is_anagram("listen", "silent")) # Output: True
23. Longest Common Prefix

import heapq def find_kth_largest(arr, k): return heapq.nlargest(k, arr)[-1] # Example usage print(find_kth_largest([3, 2, 1, 5, 6, 4], 2)) # Output: 5
25. Check if a String is a Valid Parenthesis Expression