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Data Structures & Algorithms

A collection of data structures and algorithms problems with solutions, categorized by topic. Also features so that you can practice spaced repetition and randomization of practice problems

Lists

1. Valid Parentheses[e]

2. Valid Palindrome[e]

3. Valid Anagram[e]

4. Longest Substring Without Repeating Characters[m]

5. Group Anagrams[m]

6. Encode and Decode Strings[m]

7. Longest Repeating Character Replacement[m]

8. Palindromic Substrings[m]

9. Contains Duplicate[e]

10. Two Sum[e]

11. Kth Largest Element in a Stream[e]

12. Container With Most Water[m]

13. 3Sum[m]

14. Maximum Product Subarray[m]

15. Two Sum II - Input Array Is Sorted[m]

16. Binary Search[e]

17. Guess Number Higher or Lower[e]

18. Find Smallest Letter Greater Than Target[e]

19. First Bad Version[e]

20. Search in Rotated Sorted Array[m]

21. Find First and Last Position of Element in Sorted Array[m]

22. Search in Rotated Sorted Array II[m]

23. Find Minimum in Rotated Sorted Array[m]

24. Find Minimum in Rotated Sorted Array II[m]

25. Find Peak Element[m]

26. Search a 2D Matrix[m]

27. Search a 2D Matrix II[m]

28. Kth Smallest Element in a Sorted Matrix[m]

29. Find K Closest Elements[m]

30. Koko Eating Bananas[m]

31. Capacity To Ship Packages Within D Days[m]

32. Median of Two Sorted Arrays[h]

33. Split Array Largest Sum[h]

34. Find K-th Smallest Pair Distance[h]

35. Find the Kth Smallest Product of Two Sorted Arrays[h]

36. Rotate Image[m]

37. Spiral Matrix[m]

38. Set Matrix Zeroes[m]

39. Word Search[m]

40. Linked List Cycle[e]

41. Reverse Linked List[e]

42. Merge Two Sorted Lists[e]

43. Reorder List[m]

44. Remove Nth Node From End of List[m]

45. Copy List with Random Pointer[m]

46. Add Two Numbers[m]

47. LRU Cache[m]

48. Merge k Sorted Lists[h]

49. Reverse Nodes in k-Group[h]

50. Same Tree[e]

51. Maximum Depth of Binary Tree[e]

52. Balanced Binary Tree[e]

53. Invert Binary Tree[e]

54. Lowest Common Ancestor of a Binary Search Tree[e]

55. Diameter of Binary Tree[e]

56. Subtree of Another Tree[e]

57. Validate Binary Search Tree[m]

58. Binary Tree Level Order Traversal[m]

59. Construct Binary Tree from Preorder and Inorder Traversal[m]

60. Construct Binary Tree from Inorder and Postorder Traversal[m]

61. Binary Tree Right Side View[m]

62. Implement Trie (Prefix Tree)[m]

63. Design Add and Search Words Data Structure[m]

64. Kth Smallest Element in a BST[m]

65. Lowest Common Ancestor of a Binary Tree[m]

66. Construct Binary Tree from Preorder and Postorder Traversal[m]

67. Construct Binary Search Tree from Preorder Traversal[m]

68. Count Good Nodes in Binary Tree[m]

69. Binary Tree Maximum Path Sum[h]

70. Word Search II[h]

71. Serialize and Deserialize Binary Tree[h]

72. Meeting Rooms[e]

73. Merge Intervals[m]

74. Insert Interval[m]

75. Meeting Rooms II[m]

76. Interval List Intersections[m]

77. Car Pooling[m]

78. Two Best Non-Overlapping Events[m]

79. Meeting Rooms III[h]

80. Island Perimeter[e]

81. Find the Town Judge[e]

82. Flood Fill[e]

83. Word Ladder[m]

84. Surrounded Regions[m]

85. Clone Graph[m]

86. Course Schedule[m]

87. Course Schedule II[m]

88. Minimum Height Trees[m]

89. Water and Jug Problem[m]

90. Pacific Atlantic Water Flow[m]

91. Minimum Genetic Mutation[m]

92. 01 Matrix[m]

93. Max Area of Island[m]

94. Network Delay Time[m]

95. Open the Lock[m]

96. Cheapest Flights Within K Stops[m]

97. All Paths from Source to Target[m]

98. Find Eventual Safe States[m]

99. Reachable Nodes In Subdivided Graph[m]

100. Snakes and Ladders[m]

101. Shortest Bridge[m]

102. Rotting Oranges[m]

103. Shortest Path in Binary Matrix[m]

104. As Far from Land as Possible[m]

105. Number of Closed Islands[m]

106. Number of Operations to Make Network Connected[m]

107. Find the City With the Smallest Number of Neighbors at a Threshold Distance[m]

108. Time Needed to Inform All Employees[m]

109. Minimum Time to Collect All Apples in a Tree[m]

110. Reorder Routes to Make All Paths Lead to the City Zero[m]

111. Path with Maximum Probability[m]

112. Minimum Number of Vertices to Reach All Nodes[m]

113. Maximal Network Rank[m]

114. Path With Minimum Effort[m]

115. Minimum Jumps to Reach Home[m]

116. Count Sub Islands[m]

117. Minimum Cost to Reach Destination in Time[m]

118. Check if Move is Legal[m]

119. Minimum Fuel Cost to Report to the Capital[m]

120. Minimum Score of a Path Between Two Cities[m]

121. Minimum Time to Visit Disappearing Nodes[m]

122. Last Day Where You Can Still Cross[h]

123. Minimum Window Substring[h]

124. Word Ladder II[h]

125. Reconstruct Itinerary[h]

126. Race Car[h]

127. Sum of Distances in Tree[h]

128. Shortest Path Visiting All Nodes[h]

129. Minimum Number of Days to Eat N Oranges[h]

130. Longest Path With Different Adjacent Characters[h]

131. Find Edges in Shortest Paths[h]

132. Number of Islands[m]

133. Graph Valid Tree[m]

134. Number of Islands II[m]

135. Number of Connected Components in an Undirected Graph[m]

136. Number of Provinces[m]

137. Redundant Connection[m]

138. Redundant Connection II[h]

139. Accounts Merge[m]

140. Minimize Malware Spread[m]

141. The Earliest Moment When Everyone Become Friends[m]

142. Optimize Water Distribution in a Village[m]

143. Longest Consecutive Sequence[m]

144. Find All People With Secret[h]

145. Last Stone Weight[e]

146. Swim in Rising Water[m]

147. Kth Largest Element in an Array[m]

148. Top K Frequent Elements[m]

149. Alien Dictionary[h]

150. Find Median from Data Stream[h]

151. Assign Cookies[e]

152. Lemonade Change[e]

153. Valid Parenthesis String[m]

154. Non-overlapping Intervals[m]

155. Minimum Number of Arrows to Burst Balloons[m]

156. Maximum Length of Pair Chain[m]

157. Jump Game[m]

158. Gas Station[m]

159. Hand of Straights[m]

160. Boats to Save People[m]

161. Jump Game II[m]

162. Merge Triplets to Form Target Triplet[m]

163. Partition Labels[m]

164. Subsets[e]

165. Subsets II[e]

166. Reverse String[e]

167. Binary Watch[e]

168. Subtract the Product and Sum of Digits of an Integer[e]

169. Letter Combinations of a Phone Number[m]

170. Generate Parentheses[m]

171. Next Permutation[m]

172. Valid Sudoku[m]

173. Combination Sum[m]

174. Combination Sum II[m]

175. Permutations[m]

176. Permutations II[m]

177. Combinations[m]

178. Restore IP Addresses[m]

179. Combination Sum III[m]

180. Non-decreasing Subsequences[m]

181. Letter Case Permutation[m]

182. Sudoku Solver[h]

183. N-Queens[h]

184. N-Queens II[h]

185. Word Break II[h]

186. Concatenated Words[h]

187. Factor Combinations[]

188. Generalized Abbreviation[]

189. Best Time to Buy and Sell Stock[e]

190. Climbing Stairs[e]

191. Fibonacci Number[e]

192. Min Cost Climbing Stairs[e]

193. Maximum Subarray[m]

194. Longest Palindromic Substring[m]

195. Decode Ways[m]

196. Word Break[m]

197. House Robber I[m]

198. House Robber II[m]

199. Longest Increasing Subsequence[m]

200. Coin Change[m]

201. Coin Change II[m]

202. Combination Sum IV[m]

203. Partition Equal Subset Sum[m]

204. Best Time to Buy and Sell Stock II[m]

205. Best Time to Buy and Sell Stock with Transaction Fee[m]

206. Best Time to Buy and Sell Stock with Cooldown[m]

207. Delete and Earn[m]

208. Best Time to Buy and Sell Stock V[m]

209. Best Time to Buy and Sell Stock III[h]

210. Best Time to Buy and Sell Stock IV[h]

211. Palindrome Partitioning II[h]

212. Is Subsequence[e]

213. Unique Paths[m]

214. Unique Paths II[m]

215. Minimum Path Sum[m]

216. Edit Distance[m]

217. Interleaving String[m]

218. Maximal Square[m]

219. Burst Balloons[m]

220. Longest Palindromic Subsequence[m]

221. Delete Operation for Two Strings[m]

222. Minimum ASCII Delete Sum for Two Strings[m]

223. Minimum Falling Path Sum[m]

224. Minimum Score Triangulation of Polygon[m]

225. Longest Common Subsequence[m]

226. Predict the Winner[m]

227. Unique Paths III[h]

228. Distinct Subsequences[h]

229. Single Number[e]

230. Reverse Bits[e]

231. Number of 1 Bits[e]

232. Power of Two[e]

233. Ugly Number[e]

234. Missing Number[e]

235. Power of Four[e]

236. Hamming Distance[e]

237. Binary Number with Alternating Bits[e]

238. XOR Operation in an Array[e]

239. Find the Duplicate Number[m]

240. Single Number II[m]

241. Bitwise AND of Numbers Range[m]

242. Single Number III[m]

243. Maximum Product of Word Lengths[m]

244. Counting Bits[m]

245. Sum of Two Integers[m]

246. Nth Digit[m]

247. Number Complement[m]

248. Total Hamming Distance[m]

249. Complement of Base 10 Integer[m]

250. Range Sum Query - Immutable[e]

251. Find Pivot Index[e]

252. Running Sum of 1d Array[e]

253. Product of Array Except Self[m]

254. Range Sum Query 2D - Immutable[m]

255. Maximum Size Subarray Sum Equals k[m]

256. Continuous Subarray Sum[m]

257. Subarray Sum Equals K[m]

258. Binary Subarrays With Sum[m]

259. Subarray Sums Divisible by K[m]

260. Count Number of Nice Subarrays[m]

261. Matrix Block Sum[m]

262. K Radius Subarray Averages[m]

263. Number of Submatrices That Sum to Target[h]

264. Min Stack[m]

265. Daily Temperatures[m]

266. Sliding Window Maximum[h]