207. Course Schedule Problem's Link ---------------------------------------------------------------------------- Mean: 给定一个有向图,判断是否存在top_sort序列. analyse: 转换为:判断是否存在环. 若存在环,肯定不能找到top_sort序列. 判环的方式有很多:SPFA,top_sort,BFS,DFS...随便选一种就行. Time complexity: O…

lc 207 Course Schedule 207 Course Schedule There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1…

前言 之前把一些LeetCode题目的思路写在了本子上,现在把这些全都放到博客上,以后翻阅比较方便. 题目 99.Recover Binary Search Tree 题意 Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure. 恢复两个因错误而导致的左右子树. 思路 通常我们的做法是,根据BST的特质,可以用中序遍历来检…

题目链接:Valid Sudoku | LeetCode OJ Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules. The Sudoku board could be partially filled, where empty cells are filled with the character '.'. A partially filled sudoku which is valid. Note:…

题目链接:Populating Next Right Pointers in Each Node II | LeetCode OJ Follow up for problem "Populating Next Right Pointers in Each Node". What if the given tree could be any binary tree? Would your previous solution still work? Note: You may only u…

题目链接:Populating Next Right Pointers in Each Node | LeetCode OJ Given a binary tree struct TreeLinkNode { TreeLinkNode *left; TreeLinkNode *right; TreeLinkNode *next; } Populate each next pointer to point to its next right node. If there is no next ri…

题目链接:Path Sum II | LeetCode OJ Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum. For example: Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ / \ 7 2 5 1 return [ [5,4,11,2],…

题目链接:Path Sum | LeetCode OJ Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. For example: Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11…

题目链接:Balanced Binary Tree | LeetCode OJ Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more tha…

题目链接:Same Tree | LeetCode OJ Given two binary trees, write a function to check if they are equal or not. Two binary trees are considered equal if they are structurally identical and the nodes have the same value. Tags: Depth-first Search 分析 很基本的一道深度优…