1.python解题Leetcode? + details
2.java解题src/Solution? + details
2.C++解题CPP/Solution? + details
4.特别部分random
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- Tencent - Machine learning Engineer
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- Didichuxing - Statistical Analyst
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- 字节跳动
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- HuaWei - Machine learning Engineer
核心在于匈牙利算法
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- 360 - Deep learning Engineer
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- Tencent - Deep learning Engineer
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Tencent - Deep learning Engineer
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source from:http://codeforces.com/contest/474/problem/D
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- 阿里 - Algorithm Engineer
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- 携程 - Deep learning Engineer
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- 快手2020校招
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- 搜索二叉树
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- 三个都是一个套路，以01背包进行拓展
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- Almost everytime such as Alibaba、JD、Didichuxing...
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- Hp(Hewlett-Packard) - Model Engineer
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- 蚂蚁金服
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- 阿里-推荐算法工程师
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- 阿里-数据智能技术架构师
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- source from:https://leetcode-cn.com/problems/two-sum/
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左右双指针,亮点在于定义了很多提前跳出条件，在相同值跳过的条件判断中用nums[i+1]还是nums[i-1]尤为灵活
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source from:https://leetcode-cn.com/problems/3sum/
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这题和上面一题很类似，只是最好不要在多生产变量了，直接拿num[first]+num[last]+num[i]去和target比，而不要考虑差值是否大于0，很容易绕进去
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source from:https://leetcode-cn.com/problems/3sum-closest/
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- source from:https://leetcode-cn.com/problems/4sum/
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- source from:https://leetcode-cn.com/problems/remove-element/
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search-in-rotated-sorted-array
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螺旋数组二分
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source from:https://leetcode-cn.com/problems/search-in-rotated-sorted-array/
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find-first-and-last-position-of-element-in-sorted-array
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这个考的是二分法中的while跳出条件和left、right变化逻辑，本题是找出左右边界
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source from:https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array/
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这题和上面这题很像，递归在for循环里面的回溯算法，把所有情况跑一遍。
画重点，求解过程中存着result 是List<List<Integer>>的，而tmp_list是list的,需要把tmp_list再裹一层new ArrayList<>(tmp_list)再进行add -
source from:https://leetcode-cn.com/problems/combination-sum/
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动态规划和栈的两种方法，很值得看一下
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source from:https://leetcode-cn.com/problems/trapping-rain-water/
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- source from:https://leetcode-cn.com/problems/rotate-image/
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记录上次每次可跳的最远距离
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source from:https://leetcode-cn.com/problems/jump-game/
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旋转矩阵题型，用了余数判断位置，比较亮点
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source from:https://leetcode-cn.com/problems/spiral-matrix-ii/
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- source from:https://leetcode-cn.com/problems/sort-colors/
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这题利用了python的语言机制，很有意思
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source from::https://leetcode.com/problems/subsets/
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- source from:https://leetcode-cn.com/problems/word-search/
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- 状态二维dp+值一维dp
- 半三角dp修正
- source from:https://leetcode-cn.com/problems/palindrome-partitioning-ii/
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两侧分别扫描一遍
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source from:https://leetcode-cn.com/problems/product-of-array-except-self/
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- source from:https://leetcode-cn.com/problems/move-zeroes/
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抽屉原理+环+快慢指针
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source from:https://leetcode-cn.com/problems/find-the-duplicate-number/
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find-all-duplicates-in-an-array
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和上面一样，核心是每次对abs(nums[idx])-1的处理获得nums的index很有意思
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source from:https://leetcode-cn.com/problems/find-all-duplicates-in-an-array/
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find-all-numbers-disappeared-in-an-array
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nums[abs(nums[idx]) - 1] = -abs(nums[abs(nums[idx]) - 1]),两个abs保证了所有存在的idx都被置负了
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source from:https://leetcode-cn.com/problems/find-all-numbers-disappeared-in-an-array/
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理解一下，出现次数最多的那个字母（出现次数-1）x时间窗口及为最小次数，剩余要考虑的是都为最多次数的字母数
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source from:https://leetcode-cn.com/problems/task-scheduler/
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- source from:https://leetcode-cn.com/problems/maximum-swap/
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这道题的难点在于耗时，贪心算法即可，田忌赛马，可以看下
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source from:https://leetcode-cn.com/problems/advantage-shuffle/
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- 前缀和技巧题，主要是要知道a-b能被k整除，那么有a%k==b%k
- source from:https://leetcode-cn.com/problems/subarray-sums-divisible-by-k/
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- source from:https://leetcode-cn.com/problems/height-checker/
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- 分N种情况讨论状态转移矩阵。复杂：1、转移矩阵，2、初始化逻辑
- source from:https://leetcode-cn.com/problems/regular-expression-matching/
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- source from:https://leetcode-cn.com/problems/jump-game-ii/
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中心展开，从中间值往两边展开，判断展开终止点的长度
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source from:https://leetcode-cn.com/problems/longest-palindromic-substring/
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简单递归
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source from:https://leetcode-cn.com/problems/maximum-subarray/
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- source from:https://leetcode-cn.com/problems/unique-paths/
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最优路径下的dp
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source from:https://leetcode-cn.com/problems/unique-paths-ii/
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非常基础简单的动态规划问题，适合理解动态规范的想法
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source from:https://leetcode-cn.com/problems/minimum-path-sum/
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- dp
- source from:https://leetcode-cn.com/problems/gray-code/
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状态转移方程式dp[i] = dp[i-1]+dp[i-2],复杂在什么时候加前项什么时候加后项，什么时候加两项，0的位置的考虑
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source from:https://leetcode-cn.com/problems/decode-ways/
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- 和文本编辑距离的思路很像
- source from:https://leetcode-cn.com/problems/distinct-subsequences/
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- source from:https://leetcode-cn.com/problems/triangle/
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第一轮用的traceback，时间复杂度是n的n次方，扑gai；然后我想了下，既然可以考虑回溯，为什么不能递归，其实只要把方程：flag[j] = flag[i]+s[i:j] in wordDict 这个想到就行，这个算是是像加限制性条件的dp，比如20届拼多多校招，多多鸡砍树问题
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source from:https://leetcode-cn.com/problems/word-break/
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需要存一个max和min，来做条件判断
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source from:https://leetcode-cn.com/problems/maximum-product-subarray/
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反向递归
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source from:https://leetcode-cn.com/problems/dungeon-game/
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dp算法很经典的一道题
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source from:https://leetcode-cn.com/problems/house-robber/
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- source from:https://leetcode-cn.com/problems/maximal-square/
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- source from:https://leetcode-cn.com/problems/ugly-number-ii/
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双循环的dp，同样的思路python会超时，Java不会
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source from:https://leetcode-cn.com/problems/perfect-squares/
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longest-increasing-subsequence
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dp和递归理解的好题目，值得看
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source from:https://leetcode-cn.com/problems/longest-increasing-subsequence/
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best-time-to-buy-and-sell-stock-with-cooldown
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dp的高难题，代码中带完整带解题方法
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source from:https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/
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dp的超高难题，代码中带完整带解题方法
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source from:https://leetcode-cn.com/problems/burst-balloons/
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斐波纳切动态规划
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source from:https://leetcode-cn.com/problems/coin-change/
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- source from:https://leetcode-cn.com/problems/counting-bits/
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- source from:https://leetcode-cn.com/problems/integer-break/
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01背包
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source from:https://leetcode-cn.com/problems/ones-and-zeroes/
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01背包问题，这题主要考虑提前跳出条件
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source from:https://leetcode-cn.com/problems/partition-equal-subset-sum/
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01背包+递归逻辑
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source from:https://leetcode-cn.com/problems/target-sum/
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longest-palindromic-subsequence
- 子序列通用双循环dp，这次因为涉及反推，所以用的是倒推法
- source from:https://leetcode-cn.com/problems/longest-palindromic-subsequence/
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回文子串问题
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source from:https://leetcode-cn.com/problems/palindromic-substrings/
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Partition to K Equal Sum Subsets
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依旧是递归，区别在递归逻辑在for循环中，相当于并发了n条处理逻辑，有点像树展开
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source from:https://leetcode-cn.com/problems/partition-to-k-equal-sum-subsets/
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核心在于bitmap+dp，与198题类似
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source from:https://leetcode-cn.com/problems/delete-and-earn/
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length-of-longest-fibonacci-subsequence
- 字典进行递归，以后[i,j]作为递归条件判断
- source from:https://leetcode-cn.com/problems/length-of-longest-fibonacci-subsequence/
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valid-permutations-for-di-sequence
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爱奇艺2020届校招
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source from:https://leetcode-cn.com/problems/valid-permutations-for-di-sequence/
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贪心算法概念的比较好理解的一道题
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source from:https://leetcode-cn.com/problems/video-stitching/
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hashmap+简单dp
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source from:https://leetcode-cn.com/problems/longest-string-chain/
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最简单的dp
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source from:https://leetcode-cn.com/problems/n-th-tribonacci-number/
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子序列双循环dp
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source from:https://leetcode-cn.com/problems/longest-common-subsequence/
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longest-arithmetic-subsequence-of-given-difference
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记录状态，和跳跃游戏1一样
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source from:https://leetcode-cn.com/problems/longest-arithmetic-subsequence-of-given-difference/
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二叉树中序遍历三种写法
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source from:https://leetcode-cn.com/problems/binary-tree-inorder-traversal/
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binary-tree-level-order-traversal
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二叉树层序遍历，利用了队列先进先出的性质
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source from:https://leetcode-cn.com/problems/binary-tree-level-order-traversal/
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二叉树深度计算，利用了递归性质
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source from:https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/
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二叉树合并，利用了递归性质
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source from:https://leetcode-cn.com/problems/merge-two-binary-trees/
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结点之间的最大距离，和104题的深度一样
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source from:https://leetcode-cn.com/problems/diameter-of-binary-tree/
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先遍历右子树的中序遍历，面试之前一定要看，易于理解递归在二叉树中的应用
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source from:https://leetcode-cn.com/problems/convert-bst-to-greater-tree/
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反转树，相互对称
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source from:https://leetcode-cn.com/problems/invert-binary-tree/
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tire 字典实现
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source from:https://leetcode-cn.com/problems/implement-trie-prefix-tree/
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construct-binary-tree-from-preorder-and-inorder-traversal
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360面试题，真有意思
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source from:https://leetcode-cn.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/
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serialize-and-deserialize-binary-tree
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二叉树-->list//list-->二叉树
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source from:https://leetcode-cn.com/problems/serialize-and-deserialize-binary-tree/
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lowest-common-ancestor-of-a-binary-tree
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left if right is None else right if left is None else root
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source from:https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/
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lowest-common-ancestor-of-a-binary-search-tree
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和上面一题一摸一样
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source from:https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-search-tree/
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动态规划
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source from:https://leetcode-cn.com/problems/unique-binary-search-trees/
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层次遍历
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source from:https://leetcode-cn.com/problems/symmetric-tree/
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搜索二叉树的左支<结点<右支，正好可以用中序遍历比较
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source from:https://leetcode-cn.com/problems/validate-binary-search-tree/
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类似104题、543题这种递归的方式
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source from:https://leetcode-cn.com/problems/binary-tree-maximum-path-sum/
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dfs+两数之和
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source from:https://leetcode-cn.com/problems/path-sum-iii/
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和unique-binary-search-trees这题思路一样，不同的是，unique-binary-search-trees用的是dp，本题用的是递归，核心和之前一样，[start,i]作为左树去递归，node(i)作为根，[i+1,end]作为右树去递归
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source from:https://leetcode-cn.com/problems/unique-binary-search-trees-ii/
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层序遍历改写
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source from:https://leetcode-cn.com/problems/same-tree/
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binary-tree-zigzag-level-order-traversal
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层序遍历改写
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source from:https://leetcode-cn.com/problems/binary-tree-zigzag-level-order-traversal/
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BST+中序遍历的结果是有序的,
self.ans.append(root)直接加结点，而非加值了 -
source from:https://leetcode-cn.com/problems/recover-binary-search-tree/
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基于树结构+动态规划，可谓是花哨到极点了
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source from:https://leetcode-cn.com/problems/house-robber-iii/
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binary-tree-level-order-traversal-ii
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层次遍历翻版
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source from:https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/
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convert-sorted-array-to-binary-search-tree
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有序数组-->平衡二叉树：二分查找+递归
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source from:https://leetcode-cn.com/problems/convert-sorted-array-to-binary-search-tree/
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判断是否为平衡二叉树，利用的是dfs+maximum-depth-of-binary-tree二叉树深度计算的方法
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source from:https://leetcode-cn.com/problems/balanced-binary-tree/
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source from:https://leetcode-cn.com/problems/path-sum/
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上面这两题在return的时候都做了是否是根结点的判断:
left if root.right is None else right if root.left is None else left or right
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dfs
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source from:https://leetcode-cn.com/problems/path-sum-ii/
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flatten-binary-tree-to-linked-list
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有点技巧性
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source from:https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list/
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populating-next-right-pointers-in-each-node
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跨结点直接的指向关系由root.next is not None产生
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source from:https://leetcode-cn.com/problems/populating-next-right-pointers-in-each-node/
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populating-next-right-pointers-in-each-node-ii
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与上一次递归不同，这一次因为不知道root对应的下一层是否有空结点，所以针对上一层的判断结果进行迭代
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source from:https://leetcode-cn.com/problems/populating-next-right-pointers-in-each-node-ii/
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dfs
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source from:https://leetcode-cn.com/problems/sum-root-to-leaf-numbers/
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binary-tree-preorder-traversal
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前序遍历迭代版，技巧就是queue进栈的策略是先右后左，因为前序遍历是中左右，进栈越早出栈越晚
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source from:https://leetcode-cn.com/problems/binary-tree-preorder-traversal/
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binary-tree-postorder-traversal
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巧妙的解法：宽度搜索+逆序出栈==后序输出。另外，这份代码在node = queue.pop()-->node = queue.pop(0),加个0就是层序遍历 -
source from:https://leetcode-cn.com/problems/binary-tree-postorder-traversal/
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以上两题加binary-tree-inorder-traversal都是迭代的解法，前序中序写的比较中规中矩，后序写的真的是惊艳
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层序遍历
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source from:https://leetcode-cn.com/problems/binary-tree-right-side-view/
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add-and-search-word-data-structure-design
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Tire树很经典的一道题
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source from::https://leetcode-cn.com/problems/add-and-search-word-data-structure-design/
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借鉴了上一题中的generation的写法，我觉得非常适合业务中真实使用
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source from:https://leetcode-cn.com/problems/binary-search-tree-iterator/
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dfs
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source from:https://leetcode-cn.com/problems/binary-tree-paths/
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限制性条件下的二叉树遍历计算查找，迭代要比计算更加高效
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source from:https://leetcode-cn.com/problems/sum-of-left-leaves/
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前序遍历保存，二叉搜索树的中序遍历为升序列，两则可以恢复原树
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source from:https://leetcode-cn.com/problems/serialize-and-deserialize-bst/
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看子节点的是否为None，分情况讨论
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source from:https://leetcode-cn.com/problems/delete-node-in-a-bst/
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find-mode-in-binary-search-tree
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直接遍历统计
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source from:https://leetcode-cn.com/problems/find-mode-in-binary-search-tree/
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递归求解，好题目
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source from:https://leetcode-cn.com/problems/subtree-of-another-tree/
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和binary-tree-tilt一样，计算每个结点的子树之和。
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source from:https://leetcode-cn.com/problems/most-frequent-subtree-sum/
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递归直接修改树的实现，爬楼梯的翻版
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source from:https://leetcode-cn.com/problems/add-one-row-to-tree/
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套路总结
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source from:https://leetcode-cn.com/problems/find-duplicate-subtrees/
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如果接一个
root = self.trimBST相当于对结点做一个覆盖，也就是直接修改树 -
source from:https://leetcode-cn.com/problems/trim-a-binary-search-tree/
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second-minimum-node-in-a-binary-tree
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log(h)的跳出条件的递归写法
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source from:https://leetcode-cn.com/problems/second-minimum-node-in-a-binary-tree/
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逻辑理解的递归
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source from:https://leetcode-cn.com/problems/longest-univalue-path/
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先递归到底层，然后在判断是否可以被修剪，修剪条件就是
root.val == 0 and not root.left and not root.right: -
source from:https://leetcode-cn.com/problems/binary-tree-pruning/
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smallest-subtree-with-all-the-deepest-nodes
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构造了数据对[root,depth]，用depth判断深度，用root返回depth对应的root
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source from:https://leetcode-cn.com/problems/smallest-subtree-with-all-the-deepest-nodes/
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all-possible-full-binary-trees
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基于树的动态规划，考前必看
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source from:https://leetcode-cn.com/problems/all-possible-full-binary-trees/
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check-completeness-of-a-binary-tree
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层次遍历，出现空之后不能再出现结点
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source from:https://leetcode-cn.com/problems/check-completeness-of-a-binary-tree/
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distribute-coins-in-binary-tree
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金币题，题目有点难理解，算得是每个结点的多余量，这题和jump-game神似
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source from:https://leetcode-cn.com/problems/distribute-coins-in-binary-tree/
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这题是结合了父结点+子节点递归，利用depth保存层数，parent保存子结点对应的父结点
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source from:https://leetcode-cn.com/problems/cousins-in-binary-tree/
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sum-of-root-to-leaf-binary-numbers
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^在python里面是抑或，不是次方 -
source from:https://leetcode-cn.com/problems/sum-of-root-to-leaf-binary-numbers/
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delete-nodes-and-return-forest
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复杂的dfs，在dfs的过程中对树进行修正和保存，有点难
-
source from:https://leetcode-cn.com/problems/delete-nodes-and-return-forest/
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recover-a-tree-from-preorder-traversal
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hashmap存结点，每次更新
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source from:https://leetcode-cn.com/problems/recover-a-tree-from-preorder-traversal/
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- 回溯/DFS
- source from:https://leetcode-cn.com/problems/number-of-islands/
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- dfs
- source from:https://leetcode-cn.com/problems/generate-parentheses/
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- dfs，组合题型1
- source from:https://leetcode-cn.com/problems/combination-sum/
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- dfs，组合题型2，index>start保证了双跳跃逻辑，很nice
- source from:https://leetcode-cn.com/problems/combination-sum-ii/
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- dfs，全排列升级版
- source from:https://leetcode-cn.com/problems/subsets-ii/
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- dfs，组合题型3
- source from:https://leetcode-cn.com/problems/combination-sum-iii/
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- dfs,当迭代轮数超过一次完整循环的值的时候，直接跳过
- source from:https://leetcode-cn.com/problems/permutation-sequence/
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- source from:https://leetcode-cn.com/problems/combinations/
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- dfs
- source from:https://leetcode-cn.com/problems/coin-change-2/
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maximum-length-of-a-concatenated-string-with-unique-characters
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maximum-length-of-a-concatenated-string-with-unique-characters
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evaluate-reverse-polish-notation
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栈，亮点在python 中对负数取整数部分如何操作
-
source from:https://leetcode-cn.com/problems/evaluate-reverse-polish-notation/
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辅助栈，不需要排序，仅需要知道当前最小即可
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source from:https://leetcode-cn.com/problems/min-stack/
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出入栈题，有点难想到
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source from:https://leetcode-cn.com/problems/decode-string/
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位运算
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source from:https://leetcode-cn.com/problems/divide-two-integers/
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最简单的递归，和快排，斐波纳切数列一致的写法
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source from:https://leetcode-cn.com/problems/powx-n/
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这题其实可以从右上角开始查找，会更快
-
source from::https://leetcode.com/problems/search-a-2d-matrix-ii/
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二分搜索，亮点在分组最大和变成了原数组的
[max(原数组),sum(原数组)) -
source from:https://leetcode-cn.com/problems/split-array-largest-sum/
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- source from:https://leetcode-cn.com/problems/binary-search/
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LetterCombinationsofaPhoneNumber
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这题用了dp和递归两种方法，dp更好理解也很Pythonic，递归则更加通用
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盖题递归位置在循环中，很有意思
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source from:https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/
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递归
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source from:https://leetcode-cn.com/problems/permutations/
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简单的回溯算法
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source from:https://leetcode-cn.com/problems/permutations-ii/
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地址和值；已经用ansValue用的是内存地址，时刻在变，所以要new ArrayList(ansValue)固定值使其不变
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回溯的剔除；
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source from:https://leetcode-cn.com/problems/palindrome-partitioning/
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remove-nth-node-from-end-of-list
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链表很经典的一道题
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source from::https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/
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递归算法，讲的很详细，递归复习专用
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该题递归在函数中间位置，很有意思
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source from:https://leetcode-cn.com/problems/swap-nodes-in-pairs/
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协助理解链表里面的head = head, head.next = head.next.next
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source from:https://leetcode-cn.com/problems/remove-linked-list-elements/
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递归在中间,简单题，对比上面的24题可以对比着看
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source from:https://leetcode-cn.com/problems/reverse-linked-list/
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- 翻转链表用的是迭代，参考206题reverse-linked-list
- 交换参考的是24题Swap Nodes in Pairs
- source from:https://leetcode-cn.com/problems/reverse-nodes-in-k-group/
- 深入理解地址和值
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- 快慢指针，类似题型find-the-duplicate-number
- source from:https://leetcode-cn.com/problems/linked-list-cycle/
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- 快慢指针，类似题型find-the-duplicate-number
- source from:https://leetcode-cn.com/problems/linked-list-cycle-ii/
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intersection-of-two-linked-lists
- source from:https://leetcode-cn.com/problems/intersection-of-two-linked-lists/
- 短链表+长链表<-->长链表+短链表，同等初始的结尾即为交点
-
- source from:https://leetcode-cn.com/problems/sort-list/
- 并归排序+链表
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- source from:https://leetcode-cn.com/problems/merge-k-sorted-lists/
- 和上一个很像，并归排序+链表
- 快排按照标值二分，小的在前大的在后，而归并则是按照下标二分，再分别对两个部分归并排序，先分后和，在和的过程中排序
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- source from:https://leetcode-cn.com/problems/rotate-list/
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remove-duplicates-from-sorted-list-ii
- source from:https://leetcode-cn.com/problems/remove-duplicates-from-sorted-list-ii/
- 建立一个哨兵指针，每次对比cur和cur.next的val是否一致
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remove-duplicates-from-sorted-list
- source from:https://leetcode-cn.com/problems/remove-duplicates-from-sorted-list/
- 上面一条的简单版本
-
- source from:https://leetcode-cn.com/problems/partition-list/
-
- source from:https://leetcode-cn.com/problems/reverse-linked-list-ii/
- prev.next为反转后的尾结点，正好可以接剩余结点，非常精彩
-
- source from:https://leetcode-cn.com/problems/reorder-list/
- 反转链表reverse-linked-list
-
- source from:https://leetcode-cn.com/problems/insertion-sort-list/
- 这题和remove-duplicates-from-sorted-list-ii类似，需要不停的从head结点找到比当前结点.next.val要小的结点位置
- 链表删结点方法
-
- source from:https://leetcode-cn.com/problems/delete-node-in-a-linked-list/
- 一行但是非常技巧
-
- source from:https://leetcode-cn.com/problems/add-two-numbers-ii/
- 双栈+链表
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remove-zero-sum-consecutive-nodes-from-linked-list
- source from:https://leetcode-cn.com/problems/remove-zero-sum-consecutive-nodes-from-linked-list/
- 前缀和+递归，面试前必看
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kth-largest-element-in-an-array
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加速的地方在于，维护好容量为k的小根堆之后，只需要保证根堆的根结点最小即可。
min_heap(k_min, k, 0) -
source from:https://leetcode-cn.com/problems/kth-largest-element-in-an-array/
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双端队列题目，用队列保留一个递减序列
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source from:https://leetcode-cn.com/problems/sliding-window-maximum/
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求最大：小根堆；求最小：大根堆。因为只需要保证最大最小的k个值在堆内即可，无需遍历堆。 根堆输出的时候，每次交换根堆根结点到最后，小根堆的化，数组越靠后越小，相当于降序排列；大根堆的话，数组越往后越大，相当于升序排列。
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source from:https://leetcode-cn.com/problems/top-k-frequent-elements/
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-
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数组当做双指针的一种方式
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source from:https://leetcode-cn.com/problems/summary-ranges/
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-
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双指针
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source from:https://leetcode-cn.com/problems/boats-to-save-people/
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-
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双指针
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source from:https://leetcode-cn.com/problems/fruit-into-baskets/
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-
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双指针+滑动窗口，模板要记得
-
source from:https://leetcode-cn.com/problems/minimum-window-substring/
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双指针+滑动窗口，模板要记得
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source from:https://leetcode-cn.com/problems/is-subsequence/
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-
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子集问题，双指针
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source from:https://leetcode-cn.com/problems/minimum-size-subarray-sum/
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longest-chunked-palindrome-decomposition
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回文问题，双指针
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source from:https://leetcode-cn.com/problems/longest-chunked-palindrome-decomposition/
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-
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回文问题，双指针
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source from:https://leetcode-cn.com/problems/shortest-palindrome/
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-
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区间边界解决重复，双指针
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source from:https://leetcode-cn.com/problems/subarray-product-less-than-k/
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replace-the-substring-for-balanced-string
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最优子串，双指针
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source from:https://leetcode-cn.com/problems/replace-the-substring-for-balanced-string/
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-
- source from:https://leetcode-cn.com/problems/detect-capital/
-
- source from:https://leetcode-cn.com/problems/goat-latin/
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-
有点冒泡排序的意思
-
source from:https://leetcode-cn.com/problems/orderly-queue/
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-
-
python用了最简单的递归表示，把结果表示出来再做，比较慢,所以加了@functools.lru_cache(maxsize=128, typed=False)对结果进行缓存
-
source from:https://leetcode-cn.com/problems/k-th-symbol-in-grammar/
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-
-
直接罗列全情况，排除一下就行
-
source from:https://leetcode-cn.com/problems/valid-tic-tac-toe-state/
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-
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蓄水池抽烟，randint(0,cnt)控制了每次被抛弃的概率为1/(1+cnt）
-
source from:https://leetcode-cn.com/problems/random-pick-index/
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-
- source from:https://leetcode-cn.com/problems/ugly-number/
-
- source from:https://leetcode-cn.com/problems/reach-a-number/
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-
逻辑鬼才的题目
-
source from:https://leetcode-cn.com/problems/chalkboard-xor-game/
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-
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任给三点，三角形面积等于abs(x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2))/2
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source from:https://leetcode-cn.com/problems/largest-triangle-area/
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-
-
(n-m)(n+m+1)=2N,a=n-m,b=n+m+1,a+b=2n+1,b-a=2m+1,所以a*b=2N,a,b一奇一偶
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source from:https://leetcode-cn.com/problems/consecutive-numbers-sum/
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-
-
透视图角度
-
source from:https://leetcode-cn.com/problems/surface-area-of-3d-shapes/
-
-
greatest-common-divisor-of-strings
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gcd，最大公约数；辗转相除法复习
-
source from:https://leetcode-cn.com/problems/greatest-common-divisor-of-strings/
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- 素数+回文
- source from:https://leetcode-cn.com/problems/prime-palindrome/
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- 罗列情况
- source from:https://leetcode-cn.com/problems/find-the-closest-palindrome/
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- 2N-2>N
- source from:https://leetcode-cn.com/problems/repeated-substring-pattern/
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- 平方数之和
- 二分查找
- source from:https://leetcode-cn.com/problems/sum-of-square-numbers/
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-
这题有数学解法和位解法两种，都很值得看一下
-
source from:https://leetcode.com/problems/single-number/description/
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-
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知识点1：设计一个逻辑运算，使满足存在两个变量a和b，当遍历nums的时候，对于重复元素x，第一次碰到x的时候，我们会将x赋给a，第二次碰到后再赋给b，第三次则全量抵消
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知识点2：x&~x=0
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source from:https://leetcode-cn.com/problems/single-number-ii/
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-
- source from:https://leetcode-cn.com/problems/reverse-bits/
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滑动窗口去解决字符串匹配问题
-
source from:https://leetcode-cn.com/problems/find-all-anagrams-in-a-string/
-
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substring-with-concatenation-of-all-words
- hash对比
- source from:https://leetcode-cn.com/problems/substring-with-concatenation-of-all-words/
-
- source from:https://leetcode-cn.com/problems/gas-station/
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-
转转2020届校招
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分发糖果，左右各扫一遍取max
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source from:https://leetcode-cn.com/problems/candy/
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queue-reconstruction-by-height
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原题说的是前面大于等于当前身高的，所以插矮个子不会影响排序
-
source from:https://leetcode-cn.com/problems/queue-reconstruction-by-height/
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分桶，亮点在于分N+1个桶，保证一定有一个空桶，空桶的存在保证最大间隔在桶之间，不需要再去比桶内值
-
source from:https://leetcode-cn.com/problems/maximum-gap/
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规律题，数学归纳
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source from:https://leetcode-cn.com/problems/nim-game/
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字典排序，用了python特性，也同时整理基础概念，值得去看
-
source from:https://leetcode-cn.com/problems/lexicographical-numbers/
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such that arr[i] < arr[j] < arr[k] given 0 ≤ i < j < k ≤ n-1 else return false,其中只要保证固定住最小和最大，不断降低最小值的下限，使得比最小值要大的值可以尽可能的接近最小值，从而更容易找到比接近最小值的值
-
source from:https://leetcode-cn.com/problems/increasing-triplet-subsequence/
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-
- source from:https://leetcode-cn.com/problems/relative-ranks/
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这题技巧题，理解sorted中的cmp和key的作用，key是sorted元素判断依据的接受入口，而接收值需要调用functools中的cmp_to_key进行包装，python2不用这么复杂
-
source from:https://leetcode-cn.com/problems/largest-number/
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-
- source from:https://leetcode-cn.com/problems/lru-cache/