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深度优先遍历   1．深度优先遍历的递归定义   　　假设给定图G的初态是所有顶点均未曾访问过。在G中任选一顶点v为初始出发点(源点)，则深度优先遍历可定义如下：首先访问出发点v，并将其标记为已访问过；然后依次从v出发搜索v的每个邻接点w。若w未曾访问过，则以w为新的出发点继续进行深度优先遍历，直至图中所有和源点v有路径相通的顶点(亦称为从源点可达的顶点)均已被访问为止。若

Given a 2D board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically

Given a string containing only digits, restore it by returning all possible valid IP address combinations. For example: Given "25525511135", return ["255.255.11.135", "255.255.111.35"]. (Order

题目： 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 use

题目： 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 neve

1，例子： 求树的最大深度？

题目： Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST. 解法： /** * Definition for singly-linked list. * struct ListNode { * int val

题目： Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. An example is the root-to-leaf path 1->2->3 which represents the number 123. Find

题目： Given a binary tree, find the maximum path sum. For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connecti

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. For example, If n = 4 and k = 2, a solution is: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ]