Data Structures & Algorithms Interview Questions

1. What is Big O Notation?

2. Difference Between Array and Linked List

3. What is a Hash Table?

4. What is Recursion?

5. Difference Between Stack and Queue

6. What is a Binary Search Tree (BST)?

7. What is Dynamic Programming?

8. What is a Heap?

9. BFS vs DFS: What is the Difference?

10. What is a Trie?

11. Merge Sort vs Quick Sort: What is the Difference?

12. What is a Graph?

13. What is a Doubly Linked List?

14. What is Binary Search?

15. What is a Priority Queue?

16. What is the Difference Between Time and Space Complexity?

17. What is a Balanced Tree?

18. What is the Two Pointer Technique?

19. What is the Sliding Window Technique?

20. What is Memoization?

21. What is a Circular Queue?

22. What is Topological Sort?

23. What is Dijkstra’s Algorithm?

24. What is a Red-Black Tree?

25. Greedy vs Dynamic Programming: What is the Difference?

26. What is Backtracking?

27. What is a Hash Collision?

28. What is Heap Sort?

29. What is Counting Sort?

30. What is Radix Sort?

31. What is Bucket Sort?

32. What is Insertion Sort?

33. What is Selection Sort?

34. What is Shell Sort?

35. What is Timsort?

36. What is Bubble Sort?

37. Stable vs Unstable Sort: What is the Difference?

38. Solve the Two Sum Problem

39. What is Kadane's Algorithm?

40. What is the Dutch National Flag Problem?

41. How Would You Design an LRU Cache?

42. How Do You Solve the Trapping Rain Water Problem?

43. N-Queens Problem: How Would You Solve It?

44. 0/1 Knapsack Problem: How Would You Solve It?

45. Unbounded Knapsack Problem: How Is It Different?

46. Coin Change Problem: How Would You Solve It?

47. Edit Distance Problem: How Would You Solve It?

48. How Do You Find the Longest Common Subsequence?

49. How Do You Find the Longest Increasing Subsequence?

50. How Do You Find the Longest Common Substring?

51. How Do You Solve the Subset Sum Problem?

52. How Do You Solve Partition Equal Subset Sum?

53. What is the Bellman-Ford Algorithm?

54. What is the Floyd-Warshall Algorithm?

55. What is Kruskal's Algorithm?

56. What is Prim's Algorithm?

57. What is the A* Search Algorithm?

58. What is Union-Find (Disjoint Set Union)?

59. What is Kosaraju's Algorithm?

60. What is Tarjan's Algorithm?

61. What is an AVL Tree?

62. What is a Segment Tree?

63. What is a Fenwick Tree (Binary Indexed Tree)?

64. What is a B-Tree?

65. What is a Suffix Tree?

66. What is the Lowest Common Ancestor (LCA) Problem?

67. What are Inorder, Preorder, and Postorder Tree Traversals?

68. What is Level-Order Tree Traversal?

69. What is the KMP String Matching Algorithm?

70. What is the Rabin-Karp Algorithm?

71. What is Manacher's Algorithm?

72. What is the Z-Algorithm for String Matching?

73. What is Amortized Analysis?

74. How Do You Prove a Greedy Algorithm is Correct?

75. What is the Divide and Conquer Strategy?

76. What is a Min-Heap?

77. What is a Max-Heap?

78. What is Hashing with Chaining?

79. What is Hashing with Open Addressing?

80. What is a Bloom Filter?

81. What is a Skip List?

82. What is a Splay Tree?

83. What Are the Core Bit Manipulation Operators and When Do You Use Them?

84. How Does the XOR Swap Technique Work, and Should You Actually Use It?

85. How Do You Count the Number of Set Bits in an Integer Efficiently?

86. How Do You Find the Number of Subarrays That Sum to K?

87. How Do You Find the Maximum in Every Sliding Window of Size K?

88. Minimum Window Substring: How Do You Solve It?

89. Longest Substring Without Repeating Characters

90. How Do You Solve the Valid Parentheses Problem?

91. Next Greater Element: How Do You Solve It?

92. What is the Monotonic Stack Technique?

93. What is the Monotonic Queue Technique?

94. How Do You Find the Median of Two Sorted Arrays?

95. How Do You Find the Kth Largest Element in an Array?

96. How Do You Merge K Sorted Linked Lists?

97. How Do You Reverse a Linked List in Groups of K?

98. How Do You Detect a Cycle in a Linked List?

99. What is Floyd’s Cycle Detection Algorithm?

100. How Do You Find the Middle of a Linked List?

101. How Do You Clone a Linked List with a Random Pointer?

102. How Do You Flatten a Multilevel Linked List?

103. How Would You Implement a Stack Using Queues?

104. How Would You Implement a Queue Using Stacks?

105. How Would You Design a Min Stack?

106. How Would You Evaluate Reverse Polish Notation?

107. How Does the Next Permutation Algorithm Work?

108. How Do You Rotate an Array by K Positions?

109. How Do You Rotate a Matrix 90 Degrees In Place?

110. How Do You Traverse a Matrix in Spiral Order?

111. How Do You Search in a Rotated Sorted Array?

112. How Do You Find a Peak Element in an Array?

113. What is Binary Search on the Answer?

114. What is Ternary Search?

115. What is Exponential Search?

116. What is Interpolation Search?

117. What is Jump Search?

118. Word Ladder Problem: How Would You Solve It?

119. Word Search Problem: How Would You Solve It?

120. Number of Islands Problem: How Would You Solve It?

121. What is the Flood Fill Algorithm?

122. Course Schedule Problem: How Would You Solve It?

123. What is the Graph Coloring Problem?

124. What is the Hamiltonian Path Problem?

125. What is the Traveling Salesman Problem?

126. What is a Minimum Spanning Tree?

127. How Do You Find the Shortest Path in an Unweighted Graph?

128. What is the Single-Source Shortest Path Problem?

129. What is the All-Pairs Shortest Path Problem?

130. What are Strongly Connected Components?

131. What are Articulation Points and Bridges in a Graph?

132. What is an Eulerian Path and Eulerian Circuit?

133. How Do You Check if a Graph is Bipartite?

134. How Do You Detect a Cycle in a Directed Graph?

135. How Do You Detect a Cycle in an Undirected Graph?

136. What is Topological Sort and How Does Kahn's Algorithm Work?

137. What is a Disjoint Set Union with Path Compression?

138. How Would You Build Autocomplete Using a Trie?

139. How Do You Construct a Suffix Array?

140. How Do You Find the Longest Palindromic Substring?

141. How Do You Solve the Palindrome Partitioning Problem?

142. How Does Matrix Chain Multiplication Work?

143. What is the Rod Cutting Problem?

144. What is the Egg Drop Problem?

145. What is the Boolean Parenthesization Problem?

146. What are Catalan Numbers and Their Applications?

147. How Do You Solve Fibonacci with Dynamic Programming?

148. Climbing Stairs Problem: How Do You Solve It?

149. House Robber Problem: How Do You Solve It?

150. Jump Game Problem: How Do You Solve It?

151. Word Break Problem: How Do You Solve It?

152. Decode Ways Problem: How Do You Solve It?

153. What is the Minimum Path Sum Problem?

154. What is the Unique Paths Problem?

155. What is the Maximal Square Problem?

156. How Do You Solve Largest Rectangle in Histogram?

157. What is the Container With Most Water Problem?

158. How Do You Solve the Three Sum Problem?

159. How Do You Solve the Four Sum Problem?

160. How Do You Find a Subarray With a Given Sum?

161. What is the Majority Element Problem?

162. How Does the Boyer-Moore Voting Algorithm Work?

163. What is the Quickselect Algorithm?

164. What is Reservoir Sampling?

165. What is the Fisher-Yates Shuffle Algorithm?

166. What is Morris Traversal?

167. What is a Threaded Binary Tree?

168. Red-Black Tree vs AVL Tree: What is the Difference?

169. What is a B+ Tree and Why Do Databases Use It?

170. What is a Treap and How Does It Balance Itself?

171. What is a Cartesian Tree and What Is It Used For?

172. What is a Van Emde Boas Tree and Why Is It So Fast?

173. What is the Interval Scheduling Problem?

174. How Do You Solve the Merge Intervals Problem?

175. How Do You Solve the Insert Interval Problem?

176. How Do You Solve the Meeting Rooms Problem?

177. What is the Activity Selection Problem?

178. What is the Huffman Coding Algorithm?

179. What is Job Sequencing with Deadlines?

180. What is the Fractional Knapsack Problem?

181. How Does Greedy Choice Relate to Optimal Substructure?

182. How Do You Optimize Space in Dynamic Programming?

183. Top-Down vs Bottom-Up Dynamic Programming: What is the Difference?

184. Tabulation vs Memoization: How Do They Differ in Dynamic Programming?

185. What is State Space Reduction in Dynamic Programming?

186. What is Bitmask Dynamic Programming?

187. What is Digit Dynamic Programming (Digit DP)?

188. What is Tree Dynamic Programming?

189. What is Dynamic Programming on Graphs?

190. Iterative vs Recursive Algorithms: What is the Difference?

191. What is Tail Recursion?

192. What is the Master Theorem?

193. What is a Recurrence Relation in Algorithm Analysis?

194. What Does NP-Complete Mean?

195. What is the P vs NP Problem?

196. What is the Difference Between NP-Hard and NP-Complete?

197. What are Approximation Algorithms and When Do You Use Them?

198. What are Randomized Algorithms?

199. What are Online Algorithms?

200. What is External Sorting?

201. What are Cache-Oblivious Algorithms?

202. What Makes a Data Structure Cache-Friendly?

203. What Are Lock-Free Data Structures?

204. How Would You Design a Concurrent Hash Map?

205. What is Consistent Hashing and Why is it Used?

206. What is a Count-Min Sketch and When Would You Use One?

207. Skip List vs Balanced Tree: When Would You Use Each?

208. What is Heavy-Light Decomposition?

209. What is the Sparse Table Technique?

210. What is Mo's Algorithm?

211. What are Persistent Data Structures?

212. What is a Disjoint Sparse Table?

213. Knuth-Morris-Pratt vs Rabin-Karp: What is the Difference?

214. What is the Aho-Corasick Algorithm?

215. What is a Suffix Automaton?

216. How Do You Solve the Longest Repeated Substring Problem?

217. What is String Hashing and How Is It Used?

218. Array of Arrays vs a True 2D Array: What is the Difference?

219. Static Arrays vs Dynamic Arrays: What is the Difference?

220. What is a Circular Buffer (Ring Buffer)?

221. How Would You Represent a Sparse Matrix Efficiently?

222. Adjacency List vs Adjacency Matrix: When Would You Use Each?

223. What Are the Main Graph Representation Techniques?

224. Weighted vs Unweighted Graphs: What is the Difference?

225. Directed vs Undirected Graphs: What is the Difference?

226. In-Place vs Out-of-Place Algorithms: What is the Difference?

227. Online vs Offline Algorithms: What is the Difference?