刷题（和复习）

 

08/04/2019

Category: Array

Problem #: 1. Two Sum: HashMap

15. 3Sum　: Set one target and flow from left to right

16. 3Sum Closest　: Pretty same as 3Sum but more easy

18. 4Sum　　: Pretty same as 3Sum with one more exterior loop

08/05/2019

category: Array

26. Remove Duplicates from Sorted Array　　using a fast and slow pointer Watch out for the index.

80. Remove Duplicates from Sorted Array II　　: Same as the above one with one more flag to check if there's 3 duplicates

128. LOngest Consecutive Sequence:　　set a target, from both its left and right side, find the longest consequtive sequence, withe the use of hashset. Once an element was checked, it should be removed to save time.

27. Remove Element　　The same as 26, 80

283. MOve Zeroes　　The same as above.

31. Next Permutation　　3steps, a. From right to left find the first one doesn't in ascending order, called target. b. From right to left find the first one larger than target, switch them. c. from the first right one of index of target, reverse to the end.

36. Valid SudoKu　　Using double loop and a HashSet, clearly add information of wether the particular number is in this row or  column or block. For example, if a number has already existed in this row, if another one 

also exists, it returns false.

 08/06/2019

category: Array

42. Trapping Water　　https://www.cnblogs.com/wentiliangkaihua/p/10336711.html　　1.find the peak 　　2. left to peak scan　　3. right to peak scan

48. Rotate Image　　https://www.cnblogs.com/wentiliangkaihua/p/10341704.html　　1. switch symmetrical lines（line i with line n-1-i, n is the length)　　2. Transpose（转置, switch ij with ji)

66. Plus One　　https://www.cnblogs.com/wentiliangkaihua/p/11312861.html　　1.Revesely deal with each digit, careful to carry digit.

70. Climbing Stairs https://www.cnblogs.com/wentiliangkaihua/p/10201202.html　　Iteration as what used in fibonacci. Or DP with the use of dp array.

73. Set Matrix Zeroes　　https://www.cnblogs.com/wentiliangkaihua/p/10476402.html　　The question asks O(m+n) for space instead of time. So firstly create two boolean array for column and row.

　　Scan every element, when 0 set certain array element to true. Then for row array directly scan for its true element and set other row element to 0 with Arrays.fill(matrix[i], 0)

　　For column array , if true, using an inner loop to scan each element, then the same as row array.

134. Gas Station　　https://www.cnblogs.com/wentiliangkaihua/p/10521358.html　　设置两个变量，sum判断当前的指针的有效性；total则判断整个数组是否有解，有就返回通过sum得到的下标，没有则返回-1。首先要跳过所有gas-cost小于0的点，因为从这些点永远不能开始。

135. Candy　　https://www.cnblogs.com/wentiliangkaihua/p/11313937.html　　从左到右从右到左各扫描一遍，注意从右到左时注意不要多加一（比较当前element和右+1的大小，取大值）

08/07/2019

category: Array

169. Majority Element　　https://www.cnblogs.com/wentiliangkaihua/p/10618926.html　　Solution1: Using Arrays.sort(), and return the middle one, it has to be the majority.　　Solution2: Set 1st as target, when meeting with same, count ++, else count--. The final one must be majority.

189. Rotate Array　　https://www.cnblogs.com/wentiliangkaihua/p/10693706.html　　Create a new array a[], a[(i+k) % length] = nums[i], 很巧妙

219. Contains Duplicate II　　https://www.cnblogs.com/wentiliangkaihua/p/11318840.html　　用hashmap来判决

217. Contains Duplicate 　　https://www.cnblogs.com/wentiliangkaihua/p/11318837.html　　用hashset添加元素，如果其size小于源数组就说明有duplicate

238. Product of Array Except Self　　https://www.cnblogs.com/wentiliangkaihua/p/11318843.html　　Create two arrays to store [1, a1, a1a2, a1a2a3] and [a4a3a2, a4a3, a4, 1]. Then multiply together.

334. Increasing Triplet Subsequence  　　https://www.cnblogs.com/wentiliangkaihua/p/11319072.html

206. Reverse Linked List　　https://www.cnblogs.com/wentiliangkaihua/p/10345468.html　　迭代：设置prev和cur两个指针，每次保存cur.next，一次reverse一个。递归：

 head.next.next = head;
    head.next = null;
328. Odd Even Linked List　　https://www.cnblogs.com/wentiliangkaihua/p/11320457.html Create two list: odd(based on original list) and even list. For each list, set the head and tail pointer.

 08/09/2019

category: single linked list

2. Add Two Numbers　　https://www.cnblogs.com/wentiliangkaihua/p/11136055.html　　加法的实现刚好是从最后一位开始加，先判断是否null，如果是就变0，然后相加，记录进位。用的是while循环

86. Partition List https://www.cnblogs.com/wentiliangkaihua/p/11330364.html　  Create 2 linked list , one stores value smaller than given number, the other stores equal or bigger ones. Finally the small point to the big, the big's next set to null.

92. Reverse Linked List II　　 https://www.cnblogs.com/wentiliangkaihua/p/11330583.html

 08/15/2019

category：single linked list

83. Remove Duplicates from sorted linked list　　https://www.cnblogs.com/wentiliangkaihua/p/10341623.html

82. Remove Duplicates from sorted linked list II　　https://www.cnblogs.com/wentiliangkaihua/p/11367147.html

 08/20/2019

category：single linked list

61. Rotate List https://www.cnblogs.com/wentiliangkaihua/p/11386562.html

19. Remove Nth Node From End of List　　https://www.cnblogs.com/wentiliangkaihua/p/11386565.html

24. Swap Nodes in Pairs　　https://www.cnblogs.com/wentiliangkaihua/p/10337287.html

25. Reverse Nodes in k-Group　　 https://www.cnblogs.com/wentiliangkaihua/p/10347469.html　　

08/21/2019

138. Copy List with Random Pointer　https://www.cnblogs.com/wentiliangkaihua/p/10569269.html

141. Linked List Cycle　　https://www.cnblogs.com/wentiliangkaihua/p/10541410.html 快慢指针

142. Linked List Cycle II　https://www.cnblogs.com/wentiliangkaihua/p/11392161.html 快慢指针拓展

143. Reorder List　　https://www.cnblogs.com/wentiliangkaihua/p/11392183.html

234. Palindrome Linked List　　https://www.cnblogs.com/wentiliangkaihua/p/11392187.html

Category: String

125. Valid Palindrome　　https://www.cnblogs.com/wentiliangkaihua/p/10505019.html

28. Implement strStr()　　https://www.cnblogs.com/wentiliangkaihua/p/10153583.html

 67. Add Binary　　https://www.cnblogs.com/wentiliangkaihua/p/10166689.html

08/22/2019

Category: String

 8. String to Integer (atoi)　　https://www.cnblogs.com/wentiliangkaihua/p/11397752.html

5. Longest Palindromic Substring　　https://www.cnblogs.com/wentiliangkaihua/p/11397396.html

10. Regular Expression Matching　　https://www.cnblogs.com/wentiliangkaihua/p/10353662.html

 

08/23/2019

 

Category: String

65. Valid Number　　https://www.cnblogs.com/wentiliangkaihua/p/11403201.html

14. Longest Common Prefix　　https://www.cnblogs.com/wentiliangkaihua/p/10141095.html

12. Integer to Roman　　https://www.cnblogs.com/wentiliangkaihua/p/11403393.html

13. Roman to Integer　　https://www.cnblogs.com/wentiliangkaihua/p/10141049.html

38. Count and Say　　https://www.cnblogs.com/wentiliangkaihua/p/10336371.html

49. Group Anagrams　　https://www.cnblogs.com/wentiliangkaihua/p/10349564.html

242. Valid Anagram　　https://www.cnblogs.com/wentiliangkaihua/p/11403476.html

 08/24/2019

71. Simplify Path　　https://www.cnblogs.com/wentiliangkaihua/p/11406483.html

58. Length of Last Word　　 https://www.cnblogs.com/wentiliangkaihua/p/10163224.html

205. Isomorphic Strings　　https://www.cnblogs.com/wentiliangkaihua/p/11406647.html

290. Word Pattern　　https://www.cnblogs.com/wentiliangkaihua/p/11406769.html

Category: Stack

155. Min Stack　　https://www.cnblogs.com/wentiliangkaihua/p/10612494.html

20. Valid Parentheses 　https://www.cnblogs.com/wentiliangkaihua/p/11406821.html

32. Longest Valid Parentheses　　https://www.cnblogs.com/wentiliangkaihua/p/11406881.html

08/26/2019

Category: Stack

150. Evaluate Reverse Polish Notation　　https://www.cnblogs.com/wentiliangkaihua/p/10569298.html

225. Implement Stack using Queues https://www.cnblogs.com/wentiliangkaihua/p/11415978.html

232. Implement Queue using Stacks　　https://www.cnblogs.com/wentiliangkaihua/p/11416616.html

144. Binary Tree Preorder Traversal　　https://www.cnblogs.com/wentiliangkaihua/p/11417286.html

94. Binary Tree Inorder Traversal　　https://www.cnblogs.com/wentiliangkaihua/p/10487193.html

08/27/2019

Category: Binary Tree

145. Binary Tree Postorder Traversal　　https://www.cnblogs.com/wentiliangkaihua/p/11421651.html

102. Binary Tree Level Order Traversal　　https://www.cnblogs.com/wentiliangkaihua/p/10493584.html

107. Binary Tree Level Order Traversal II　　上面的用Collections.reverse()即可

199. Binary Tree Right Side View　　https://www.cnblogs.com/wentiliangkaihua/p/11421681.html　　也是level order view上改动

226. Invert Binary Tree　 　　层层遍历或递归

08/28/2019

Category: Binary Tree

遇到BST就要想起inorder，因为inorder下BST以从小到大排列。

173. Binary Search Tree Iterator　 Iterator包含next和hasNext方法，返回最小的elemengt就是求中序遍历

103. Binary Tree Zigzag Level Order Traversal 　　Level Order traverse的变种，可以①先levelorder然后偶数level reverse，也可以②设置一个boolean 变量isLeftRight，每到下一层就取反，然后add(0, val)保证是reverse。

 08/29/2019

Category: Binary Tree

100. Same Tree　　https://www.cnblogs.com/wentiliangkaihua/p/11432823.html

104. Maximum Depth of Binary Tree　　https://www.cnblogs.com/wentiliangkaihua/p/10504051.html

110. Balanced Binary Tree　　https://www.cnblogs.com/wentiliangkaihua/p/11432879.html

114. Flatten Binary Tree to Linked List　　https://www.cnblogs.com/wentiliangkaihua/p/11434149.html

116. Populating Next Right Pointers in Each Node　　https://www.cnblogs.com/wentiliangkaihua/p/10509641.html

 08/30/2019

Category: Binary Tree

105. Construct Binary Tree from Preorder and Inorder Traversal　　https://www.cnblogs.com/wentiliangkaihua/p/10504054.html

08/30/2019

Category: Binary Tree

106. Construct Binary Tree from Inorder and Postorder Traversal　　https://www.cnblogs.com/wentiliangkaihua/p/11441287.html

09/01/2019

Category: Binary Tree

98. Validate Binary Search Tree　　https://www.cnblogs.com/wentiliangkaihua/p/10528207.html

108. Convert Sorted Array to Binary Search Tree　　https://www.cnblogs.com/wentiliangkaihua/p/10504814.html

109. Convert Sorted List to Binary Search Tree　　https://www.cnblogs.com/wentiliangkaihua/p/11444486.html

235. Lowest Common Ancestor of a Binary Search Tree　　https://www.cnblogs.com/wentiliangkaihua/p/11444491.html

09/02/2019

Category: Binary Tree

230. Kth Smallest Element in a BST

09/03/2019

Category: Binary Tree

111. Minimum Depth of Binary Tree　　https://www.cnblogs.com/wentiliangkaihua/p/10504058.html

112. Path Sum　　https://www.cnblogs.com/wentiliangkaihua/p/11456721.html

113. Path Sum II　　https://www.cnblogs.com/wentiliangkaihua/p/11456997.html

09/04/2019

Category: Binary Tree

124. Binary Tree Maximum Path Sum https://www.cnblogs.com/wentiliangkaihua/p/11462725.html

117. Populating Next Right Pointers in Each Node II　　https://www.cnblogs.com/wentiliangkaihua/p/11462748.html

129. Sum Root to Leaf Numbers　　https://www.cnblogs.com/wentiliangkaihua/p/11463090.html

236. Lowest Common Ancestor of a Binary Tree　　https://www.cnblogs.com/wentiliangkaihua/p/11463514.html

09/06/2019

Category: 排序

147. Insertion Sort List　　https://www.cnblogs.com/wentiliangkaihua/p/11470740.html

21. Merge Two Sorted Lists　　https://www.cnblogs.com/wentiliangkaihua/p/11470834.html

88. Merge Sorted Array　　https://www.cnblogs.com/wentiliangkaihua/p/10354377.html

09/09/2019

Category: 排序

75. Sort Colors　　https://www.cnblogs.com/wentiliangkaihua/p/10328623.html

215. Kth Largest Element in an Array　　https://www.cnblogs.com/wentiliangkaihua/p/11495232.html

41. First Missing Positive　　https://www.cnblogs.com/wentiliangkaihua/p/10349524.html

274. H-Index　　https://www.cnblogs.com/wentiliangkaihua/p/11496922.html

09/10/2019

Category: 排序

164. Maximum Gap　　https://www.cnblogs.com/wentiliangkaihua/p/11504112.html

179. Largest Number　　https://www.cnblogs.com/wentiliangkaihua/p/10687369.html

34. Find First and Last Position of Element in Sorted Array　　https://www.cnblogs.com/wentiliangkaihua/p/10332409.html

35. Search Insert Position　　https://www.cnblogs.com/wentiliangkaihua/p/11505397.html

09/11/2019

Category: search

33. Search in Rotated Sorted Array　　https://www.cnblogs.com/grandyang/p/4325648.html

81. Search in Rotated Sorted Array II　　https://www.cnblogs.com/wentiliangkaihua/p/11510998.html

74. Search a 2D Matrix 　　https://www.cnblogs.com/wentiliangkaihua/p/11511268.html

240. Search a 2D Matrix II　　https://www.cnblogs.com/wentiliangkaihua/p/11511373.html

09/12/2019

Category: search

153. Find Minimum in Rotated Sorted Array　　https://www.cnblogs.com/wentiliangkaihua/p/11516045.html

154. Find Minimum in Rotated Sorted Array II　　https://www.cnblogs.com/wentiliangkaihua/p/11516050.html

09/14/2019

Category: search

275. H-index II　　https://www.cnblogs.com/wentiliangkaihua/p/11521488.html

09/16/2019

78. Subsets　　https://www.cnblogs.com/wentiliangkaihua/p/10367908.html

90. Subsets II　　https://www.cnblogs.com/wentiliangkaihua/p/11533090.html

09/17/2019

46. Permutations

47. Permutations II

77. COmbinations　　https://www.cnblogs.com/wentiliangkaihua/p/11538277.html

17. Letter Combinations of a Phone Number　　https://www.cnblogs.com/wentiliangkaihua/p/10294161.html

09/18/2019

127. Word Ladder　　https://www.cnblogs.com/wentiliangkaihua/p/11546553.html

306. Additive Number

130. Surrounded Regions　　https://www.cnblogs.com/wentiliangkaihua/p/11548811.html

09/19/2019

DFS：

131. Palindrome Partitioning　　https://www.cnblogs.com/wentiliangkaihua/p/10516126.html

62. Unique Paths　　https://www.cnblogs.com/wentiliangkaihua/p/11553565.html

63. Unique Paths II　　https://www.cnblogs.com/wentiliangkaihua/p/11553586.html
51. N-Queens　　https://www.cnblogs.com/wentiliangkaihua/p/10487182.html

52. N-Queens II　　https://www.cnblogs.com/wentiliangkaihua/p/11555191.html

09/20/2019

DFS：

93. Restore IP Addresses　　https://www.cnblogs.com/wentiliangkaihua/p/11560427.html

39. Combination Sum

40. Combination Sum II

09/21/2019

DFS：

216. Combination Sum III　　https://www.cnblogs.com/wentiliangkaihua/p/11570250.html

09/23/2019

22. Generate Parentheses　　https://www.cnblogs.com/wentiliangkaihua/p/10290658.html

36. Valid Sudoku　　https://www.cnblogs.com/wentiliangkaihua/p/10332455.html

37. Sudoku Solver

 09/24/2019

79. Word Search　　很多边界条件　　https://www.cnblogs.com/wentiliangkaihua/p/10482687.html

50. Pow(x, n)　　https://www.cnblogs.com/wentiliangkaihua/p/10354756.html

69. Sqrt(x)　　https://www.cnblogs.com/wentiliangkaihua/p/10177246.html

55. Jump Game　　https://www.cnblogs.com/wentiliangkaihua/p/10355826.html　　动态规划，贪心（从前到后，从后往前）

45. Jump Game II　　https://www.cnblogs.com/wentiliangkaihua/p/11583565.html　贪心

09/25/2019

121. Best Time to Buy and Sell Stock 　　https://www.cnblogs.com/wentiliangkaihua/p/10386673.html 记录两个值

122. Best Time to Buy and Sell Stock II　　https://www.cnblogs.com/wentiliangkaihua/p/10504917.html 加起来

3. Longest Substring Without Repeating Characters　　https://www.cnblogs.com/wentiliangkaihua/p/10204173.html start，ans每次检查更新

11. Container With Most Water　　https://www.cnblogs.com/wentiliangkaihua/p/11589804.html、双指针法

09/26/2019

330. Patching Array　　https://www.cnblogs.com/wentiliangkaihua/p/11595476.html

120. Triangle　　https://www.cnblogs.com/wentiliangkaihua/p/11595506.html

53. Maximum Subarray　　https://www.cnblogs.com/wentiliangkaihua/p/10163216.html

152. Maximum Product Subarray　　https://www.cnblogs.com/wentiliangkaihua/p/10597915.html

09/27/2019

Dynamic Programming

96. Unique Binary Search Trees　　https://www.cnblogs.com/wentiliangkaihua/p/11601268.html

322. Coin Change　　https://www.cnblogs.com/wentiliangkaihua/p/11601293.html

300. Longest Increasing Subsequence 　　https://www.cnblogs.com/wentiliangkaihua/p/11601660.html

10/04/2019

132.  Palindrome Partitioning II　　 https://www.cnblogs.com/wentiliangkaihua/p/11624192.html　　

1207. Unique Number of Occurrences hashmap.values是一个collections，可以用arraylist变成list

10/07/2019

123. Best Time to Buy and Sell Stock III　　https://www.cnblogs.com/wentiliangkaihua/p/11633310.html

10/09/2019

84. Largest Rectangle in Histogram　　https://www.cnblogs.com/wentiliangkaihua/p/10527833.html

85. Maximal Rectangle　　https://www.cnblogs.com/wentiliangkaihua/p/11645722.html

买卖股票　　http://www.360doc.com/content/16/1004/16/10408243_595735141.shtml

188. Best Time to Buy and Sell Stock IV　　https://www.cnblogs.com/wentiliangkaihua/p/11647127.html

10/10/2019

309. Best Time to Buy and Sell Stock with Cooldown　　https://www.cnblogs.com/wentiliangkaihua/p/11653207.html

10/11/2019

 64. Minimum Path Sum　　https://www.cnblogs.com/wentiliangkaihua/p/10487183.html

97. Interleaving String　　https://www.cnblogs.com/wentiliangkaihua/p/11658025.html

10/14/2019

72. Edit Distance　　https://www.cnblogs.com/wentiliangkaihua/p/11676110.html

91. Decode Ways　　https://www.cnblogs.com/wentiliangkaihua/p/11677104.html

10/15/2019

115. Distinct Subsequences　　https://www.cnblogs.com/wentiliangkaihua/p/11682193.html

139. Word Break　　https://www.cnblogs.com/wentiliangkaihua/p/10529133.html

10/16/2019

44. Wildcard Matching　　https://www.cnblogs.com/wentiliangkaihua/p/11689635.html

174. Dungeon Game　　https://www.cnblogs.com/wentiliangkaihua/p/11689711.html

198. House Robber　　https://www.cnblogs.com/wentiliangkaihua/p/10693760.html

213. House Robber II　　https://www.cnblogs.com/wentiliangkaihua/p/11690008.html

337. House Robber III　　https://www.cnblogs.com/wentiliangkaihua/p/11690409.html

303. Range Sum Query - Immutable　　https://www.cnblogs.com/wentiliangkaihua/p/11691017.html

304. Range Sum Query 2D - Immutable　　https://www.cnblogs.com/wentiliangkaihua/p/11691352.html

10/18/2019

133. Clone Graph　　https://www.cnblogs.com/wentiliangkaihua/p/11701682.html

190. Reverse Bits　　https://www.cnblogs.com/wentiliangkaihua/p/10693746.html

187. Repeated DNA Sequences　　https://www.cnblogs.com/wentiliangkaihua/p/11701690.html

191. Number of 1 Bits　　https://www.cnblogs.com/wentiliangkaihua/p/10693747.html

136. Single Number　　https://www.cnblogs.com/wentiliangkaihua/p/10521657.html

137. Single Number II　　https://www.cnblogs.com/wentiliangkaihua/p/10522060.html

260. Single Number III　　https://www.cnblogs.com/wentiliangkaihua/p/11702705.html

231. Power of Two　　https://www.cnblogs.com/wentiliangkaihua/p/11702711.html

326. Power of Three　　https://www.cnblogs.com/wentiliangkaihua/p/11702718.html

342. Power of Four　　https://www.cnblogs.com/wentiliangkaihua/p/11702720.html

268. Missing Number　　https://www.cnblogs.com/wentiliangkaihua/p/11702723.html