This is the answer of some questions in LeetCode
I will try my best to update it !
43 answers are already done~
- NO.1 Two Sum
暴力双循环
哈希表增加空间换取时间增速
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NO.7 Reverse Integer
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NO.9 Palindrome Number
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NO.13 Rome to Integer
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NO.14 Longest Common Prefix
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NO.20 Valid Parentheses
This easy 20 is a little hard [upset]
- NO.21 Merge Two Sorted Lists
Python has to stimulate the structure of ListNode which I'm not fimiliar
- NO.26 Remove Duplicates from Sorted Array
Have learned some new thing in this one !
- NO.27 Remove Element
Another one about list.remove()!
- NO.28 Implement strStr()
list[0:0] is []
str.find(str2,begin,end = len(str))
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NO.35 Search Insert Position
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NO.38 Count And Say
I use a subtle method to fix boundary problem in loops
- NO.53 Maximum Subarray (DP)
The first DP quiz
- NO.58 Length of Last Word
range(len(s)-1,-1,-1) loop from the back direction
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NO.66 Plus One
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NO.67 Add Binary
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NO.237 Delete Node in a Linked List
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NO.70 Climbing Stairs
Fibonacci sequence!
- NO.104 Maximum Depth of Binary Tree
遍历二叉树，迭代和递归！第一道DFS深度优先搜索题~
- NO.121 Best Time to Buy and Sell Stock
股票类第一题，双指针循环！一个记录最小cost一个记录当前profit
- NO.292 Nim Game
Nim游戏，4的倍数先手必输，反之先手必赢
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NO.344 Reverse String
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NO.557 Reverse Words in a String III
字符串不可变，常见的操作只有切片和索引
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NO.206 Reverse Linked List
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NO. 136 Single Number
异或（^） 二进制数的异或运算有如下性质：
a ^ a = 0
a ^ 0 = a;
a ^ b ^ a = a ^ a ^ b- NO.141 Linked List Cycle
快慢指针判断环
哈希表判断环
置空法判断环
- NO.235 Lowest Common Ancestor of a Binary Search Tree
二分搜索树的递归查找
- NO.169 Majority Element
这里有一个优秀算法：投票法，时间复杂度为$O(n)$,空间复杂度为$O(1)$
- NO.122 Best Time to Buy and Sell Stock II
DP 第二题，动态规划最重要的一步是要确定状态是什么，然后写出状态转移方程
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NO.217 Contains Duplicate
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NO.88 Merge Sorted Array
归并排序，理清尾部的逻辑很重要！
- NO.155 Min Stack
用 list 模拟 stack
- NO.231 Power of Two
按位与的操作很巧妙
- NO.160 Intersection of Two Linked Lists
双指针，8字法！
- NO.415 Add Strings
模拟加法过程
- NO.8 String to Integer (atoi)
一手贼溜的正则表达式
- NO.15 3Sum
Two Sum 的升级版，必须用排序加对撞指针解决
大概断更了10天，做了一些别的事情，现在站在人生的三岔口，觉得广阔的天地充满希望可又十分凶险，希望我能坚持奋斗，找到自己热爱的东西，通过自律达到自由！
- NO.5 Longest Palindromic Substring
动态规划判断回文字符串
- NO.2 Add Two Numbers
链表实现的加法，进位操作值得注意
- NO.11 Container With Most Water
双指针法加速，一次循环丢弃多余状态，体现了算法的威力！
- NO.16 3Sum Closest
排序 + 对撞指针 + 损失函数(目标函数)
- NO.33
二分查找法，时间复杂度为$O(log_2n)$，空间复杂度最小可为$O(1)$
二分查找法编程模版 非常细致，值得详细钻研
Python 内置的
in方法采用的应当就是二分查找
- NO.43 Multiply String
模拟乘法过程，时间复杂度$O(m+n)$
- NO.46 Permutations(排列)
回溯法，递归实现,时间复杂度略快于$O(n \times n!)$，慢于$O(n!)$，空间复杂度为$O(n!)$