TODO

效率可以高起来的，2～3小时5题，平时那是在磨洋工

Not very clear, need to re-study

~~134, gas station问题，最终解决了，是用的猜想方法来加速~~
94, 树的遍历的非递归算法，用stack存轨迹
15, 3SUM(2sum)时，two pointers的使用，双向移动
98, 类似树的中序遍历，存一个pre节点用于比较BST
130, Union-find
143, 属于“智力“题，考操作，算是我不太喜欢的题型
127, Word Ladder, 想破脑袋不会
114, 递归函数的理解和写法，实际运行栈图解分析
11, 双指针
137, 什么ones, twos, 模拟三进制

Multiple algorithms, need to re-study

22,
53, 很有意思，有助于理解DP
93, backtracking 和 DFS的关系?
55, 别人算法里面的逻辑？贪心而不是DP?
80, 最多允许存2次
28, 他们怎样使得code如此简洁?
15, 2sum::two pointers的使用，o(n^2)->o(n)
90, 组合问题中有重复元素，DP，backtracking, etc.
119,120, DP的bottom up简化了问题，并且注意倒序可避免旧值覆盖
139, DP的另一种写法，倒着推，和LinearPartion很像
114, DFS然后别人第一种写法递归很简洁，第二种方法非递归且空间为o(1)
112, backtracking在tree中的应用，mark
129, 非常好的一题，分治时注意看如何将上面的值朝下传
Regular Expression, 考虑三种写法怎么转换，recursive，memorization，dp

Note

2和67避免重复写代码，使用 while(l1||l2||carry)
121使用一个for动态记录前面的最小，并且计算当前的最大差值，很巧妙
39 combination用backtracking，条件不是cnt而是nums[i]<=target
14, 看起来复杂，但实质简单
300, DP思想扫除定势，返回值并不一定是dp[n]，比如此处需要遍历找max dp[i]
53, maxEndinghere的想法很好，和300一样，最终结果是dp过程中的最大值maxSofar,并且可优化空间
9, 学到的是要think from 抽象的层面，不要去利用最底层的特性作为算法，此谓”算法“。
35, 可以作为使用custom二分搜索的基础示例
156, 传值方式，一直到最低，然后组层上传，在传值的同时对这一层的结构做一些变换
361, 419联系起来，把左边和上边当墙，把左上角当做一段起点的标志，w是起点
378, 373 取出最小的然后放进去一个比它大的，这样k次得到k序列
333,366 后序访问 recursive倒着向上传值，传值的过程中还可以做其他事
386 树的方法，preorder，还有插入res中的顺序也很赞，一次到位
［思想］84，378, 373共同点是有种不变量的感觉，84题栈中前面的都比它小（大的都弹出去了），后面比它大，直到当前i也比它小，这样找到了两个边界
［方法］282. Expression Add Operators 和227. Basic Calculator II中对没有等号的式子的计算，要多增加一个量pre来处理乘除法。
[方法]285 用两个栈分别实现bst中nextPre和nextSucc，类似Closest Binary Search Tree Value II；另外inorder和reverse inorder
437Path Sum III, 抽象思维，而不是传值下去解

Name		Name	Last commit message	Last commit date
Latest commit History 289 Commits
basic		basic
collections		collections
.gitignore		.gitignore
1. Two Sum.cpp		1. Two Sum.cpp
100.Same Tree.cpp		100.Same Tree.cpp
101. Symmetric Tree.cpp		101. Symmetric Tree.cpp
102. Binary Tree Level Order Traversal.cpp		102. Binary Tree Level Order Traversal.cpp
103. Binary Tree Zigzag Level Order Traversal.cpp		103. Binary Tree Zigzag Level Order Traversal.cpp
104. Maximum Depth of Binary Tree.cpp		104. Maximum Depth of Binary Tree.cpp
105. Construct Binary Tree from Preorder and Inorder Traversal.cpp		105. Construct Binary Tree from Preorder and Inorder Traversal.cpp
106. Construct Binary Tree from Inorder and Postorder Traversal.cpp		106. Construct Binary Tree from Inorder and Postorder Traversal.cpp
107. Binary Tree Level Order Traversal II.cpp		107. Binary Tree Level Order Traversal II.cpp
108. Convert Sorted Array to Binary Search Tree.cpp		108. Convert Sorted Array to Binary Search Tree.cpp
109. Convert Sorted List to Binary Search Tree.cpp		109. Convert Sorted List to Binary Search Tree.cpp
11. Container With Most Water.cpp		11. Container With Most Water.cpp
110.Balanced Binary Tree.cpp		110.Balanced Binary Tree.cpp
111.Minimum Depth of Binary Tree.cpp		111.Minimum Depth of Binary Tree.cpp
112. Path Sum.cpp		112. Path Sum.cpp
113. Path Sum II.cpp		113. Path Sum II.cpp
114. Flatten Binary Tree to Linked List.cpp		114. Flatten Binary Tree to Linked List.cpp
116. Populating Next Right Pointers in Each Node.cpp		116. Populating Next Right Pointers in Each Node.cpp
118. Pascal's Triangle.cpp		118. Pascal's Triangle.cpp
119. Pascal's Triangle II.cpp		119. Pascal's Triangle II.cpp
12. Integer to Roman.cpp		12. Integer to Roman.cpp
120. Triangle.cpp		120. Triangle.cpp
121. Best Time to Buy and Sell Stock.cpp		121. Best Time to Buy and Sell Stock.cpp
122. Best Time to Buy and Sell Stock II.cpp		122. Best Time to Buy and Sell Stock II.cpp
125. Valid Palindrome.cpp		125. Valid Palindrome.cpp
129.Sum-Root-to-Leaf-Numbers.cpp		129.Sum-Root-to-Leaf-Numbers.cpp
13. Roman to Integer.cpp		13. Roman to Integer.cpp
131. Palindrome Partitioning.cpp		131. Palindrome Partitioning.cpp
134. Gas Station.cpp		134. Gas Station.cpp
136. Single Number.cpp		136. Single Number.cpp
137. Single Number II.cpp		137. Single Number II.cpp
139. Word Break.cpp		139. Word Break.cpp
14. Longest Common Prefix.cpp		14. Longest Common Prefix.cpp
141. Linked List Cycle.cpp		141. Linked List Cycle.cpp
142. Linked List Cycle II.cpp		142. Linked List Cycle II.cpp
143. Reorder List.cpp		143. Reorder List.cpp
144. Binary Tree Preorder Traversal.cpp		144. Binary Tree Preorder Traversal.cpp
145.Binary Tree Postorder Traversal.cpp		145.Binary Tree Postorder Traversal.cpp
146.-LRU-Cache.cpp		146.-LRU-Cache.cpp
148. Sort List.cpp		148. Sort List.cpp
15. 3Sum.cpp		15. 3Sum.cpp
150. Evaluate Reverse Polish Notation.cpp		150. Evaluate Reverse Polish Notation.cpp
155. Min Stack.cpp		155. Min Stack.cpp
16. 3Sum Closest.cpp		16. 3Sum Closest.cpp
160. Intersection of Two Linked Lists.cpp		160. Intersection of Two Linked Lists.cpp
162. Find Peak Element.cpp		162. Find Peak Element.cpp
165. Compare Version Numbers.cpp		165. Compare Version Numbers.cpp
169. Majority Element.cpp		169. Majority Element.cpp
17. Letter Combinations of a Phone Number.cpp		17. Letter Combinations of a Phone Number.cpp
179.Largest Number.cpp		179.Largest Number.cpp
18. 4Sum.cpp		18. 4Sum.cpp
189. Rotate Array.cpp		189. Rotate Array.cpp
19. Remove Nth Node From End of List.cpp		19. Remove Nth Node From End of List.cpp
191. Number of 1 Bits.cpp		191. Number of 1 Bits.cpp
198. House Robber.cpp		198. House Robber.cpp
2. Add Two Numbers.cpp		2. Add Two Numbers.cpp
20. Valid Parentheses.cpp		20. Valid Parentheses.cpp
200. Number of islands.cpp		200. Number of islands.cpp
202. Happy Number.cpp		202. Happy Number.cpp
206. Reverse Linked List.cpp		206. Reverse Linked List.cpp
208.Implement Trie (Prefix Tree).cpp		208.Implement Trie (Prefix Tree).cpp
21. Merge Two Sorted Lists.cpp		21. Merge Two Sorted Lists.cpp
213. House Robber II.cpp		213. House Robber II.cpp
216. Combination Sum III.cpp		216. Combination Sum III.cpp
217.Contains Duplicate.cpp		217.Contains Duplicate.cpp
22. Generate Parentheses.cpp		22. Generate Parentheses.cpp
220. Contains Duplicate III.cpp		220. Contains Duplicate III.cpp
237. Delete Node in a Linked List.cpp		237. Delete Node in a Linked List.cpp
24. Swap Nodes in Pairs.cpp		24. Swap Nodes in Pairs.cpp
242. Valid Anagram.cpp		242. Valid Anagram.cpp
257. Binary Tree Paths.cpp		257. Binary Tree Paths.cpp
258. Add Digits 2.cpp		258. Add Digits 2.cpp
258. Add Digits.cpp		258. Add Digits.cpp
26. Remove Duplicates from Sorted Array.cpp		26. Remove Duplicates from Sorted Array.cpp
263. Ugly Number.cpp		263. Ugly Number.cpp
27. Remove Element.cpp		27. Remove Element.cpp
273. Integer to English Words 2.cpp		273. Integer to English Words 2.cpp
273. Integer to English Words.cpp		273. Integer to English Words.cpp
28. Implement strStr().cpp		28. Implement strStr().cpp
283. Move Zeroes.cpp		283. Move Zeroes.cpp
29. Divide Two Integers.cpp		29. Divide Two Integers.cpp
3. Longest Substring Without Repeating Characters.cpp		3. Longest Substring Without Repeating Characters.cpp
300. Longest Increasing Subsequence.cpp		300. Longest Increasing Subsequence.cpp
303. Range Sum Query - Immutable.cpp		303. Range Sum Query - Immutable.cpp
31. Next Permutation.cpp		31. Next Permutation.cpp
34. Search for a Range.cpp		34. Search for a Range.cpp
35. Search Insert Position.cpp		35. Search Insert Position.cpp
36. Valid Sudoku.cpp		36. Valid Sudoku.cpp
38. Count and Say.cpp		38. Count and Say.cpp
39. Combination Sum.cpp		39. Combination Sum.cpp
40. Combination Sum II.cpp		40. Combination Sum II.cpp
43. Multiply Strings.cpp		43. Multiply Strings.cpp
44. Wildcard Matching.cpp		44. Wildcard Matching.cpp
46. Permutations.cpp		46. Permutations.cpp
47. Permutations II.cpp		47. Permutations II.cpp
48. Rotate Image.cpp		48. Rotate Image.cpp
5. Longest Palindromic Substring.cpp		5. Longest Palindromic Substring.cpp

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