lemonade13的博客

git非常常用，但是一直没有系统地了解过它的原理，此篇借助https://learngitbranching.js.org/?locale=zh_CN来练习git命令，记录每个关卡练习后对该命令的理解。 基础命令 git commit：提交改动到当前分支（默认为master）。 git branch a：新建名为a的分支。 git checkout a：head指针切换到a分支，当前分支为...

52. N-Queens II Then-queens puzzle is the problem of placingnqueens on ann×nchessboard such that no two queens attack each other. Given an integern, return the number ofdistinct solutions t...

比赛链接：https://leetcode-cn.com/contest/weekly-contest-178/ 赛后总结 这场比赛打得不太顺，可能是和最近写代码思路很卡有关？这周刷的是回溯法，刷到二维平面还处在很难受的阶段。 不过提升是缓慢的，量变积累质变嘛。 第一题：总体思路还是清晰的，用了大概十分钟。还可以更快更熟练。 第二题：这道题不难，和第一题的思路类似，只是过程复杂一些。选择...

77. Combinations Given two integersnandk, return all possible combinations ofknumbers out of 1 ...n. Example: Input:n = 4, k = 2 Output: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1...

46. Permutations Given a collection ofdistinctintegers, return all possible permutations. Example: Input: [1,2,3] Output: [ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1] ] 题目...

131. Palindrome Partitioning Given a strings, partitionssuch that every substring of the partition is a palindrome. Return all possible palindrome partitioning ofs. Example: Input:"aab" Outp...

17. Letter Combinations of a Phone Number Given a string containing digits from2-9inclusive, return all possible letter combinations that the number could represent. A mapping of digit to letters ...

同样是求最低公共祖先的题，在不同的树的条件下，思路有差别。 对于树的题，都同时可以同递归和非递归方法实现。 1.BST 最简单的类型，详见：235.Lowest Common Ancestor of a Binary Search Tree 时间O(logn)，空间O(1)。 2.普通树，有父节点指针 先分别找到目标节点，再逆向走父节点指针取出路径，问题转而求两个链表的第一个公...

参考：https://www.cnblogs.com/engineerLF/p/5393006.html

98.Validate Binary Search Tree Given a binary tree, determine if it is a valid binary search tree (BST). Assume a BST is defined as follows: The left subtree of a node contains only nodes with key...

437.Path Sum III You are given a binary tree in which each node contains an integer value. Find the number of paths that sum to a given value. The path does not need to start or end at the root or...

129.Sum Root to Leaf Numbers Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number. An example is the root-to-leaf path1->2->3which represents...

126. Word Ladder II Given two words (beginWordandendWord), and a dictionary's word list, find all shortest transformation sequence(s) frombeginWordtoendWord, such that: Only one letter can be c...

113.Path Sum II Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum. Note:A leaf is a node with no children. Example: Given the below binary tre...