问题描述: Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree is symmetric: 1 / \ 2 2 / \ / \ 3 4 4 3 But the following is not: 1 / \ 2 2 \ \ 3 3 Note:Bonus points if you could solv…

这是悦乐书的第163次更新,第165篇原创 01 看题和准备 今天介绍的是LeetCode算法题中Easy级别的第22题(顺位题号是101).给定二叉树,检查它是否是自身的镜像(即,围绕其中心对称). 例如,这个二叉树[1,2,2,3,4,4,3]是对称的: 1 / \ 2 2 / \ / \ 3 4 4 3 但是以下[1,2,2,null,3,null,3]不是: 1 / \ 2 2 \ \ 3 3 本次解题使用的开发工具是eclipse,jdk使用的版本是1.8,环境是win7 64位系统,…

Problem description: http://oj.leetcode.com/problems/symmetric-tree/ Basic idea: Both recursive and iterative solutions. Iterative solution: /** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNo…

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). For example, this binary tree is symmetric: 1 / \ 2 2 / \ / \ 3 4 4 3 But the following is not: 1 / \ 2 2 \ \ 3 3 题意就是给定一个二叉树,判定它是否是自己的镜像,这道题我一开始想着只求一下中序序列…

题目: Two elements of a binary search tree (BST) are swapped by mistake. Recover the tree without changing its structure. Note: A solution using O(n) space is pretty straight forward. Could you devise a constant space solution? 题解: 解决方法是利用中序遍历找顺序不对的两个点…

题目: 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 keys less than the node's key. The right subtree of a node contains only nodes with…

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 never differ by more than 1. 题解: 采用递归的方法,要记录depth用来比较. 代码如下:…

题目: Given an array where elements are sorted in ascending order, convert it to a height balanced BST. 题解: 先复习下什么是二叉搜索树(引自Wikipedia): 二叉查找树(Binary Search Tree),也称有序二叉树(ordered binary tree),排序二叉树(sorted binary tree),是指一棵空树或者具有下列性质的二叉树: 若任意节点的左子树不空,则左子树…

题目: Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node. 题解: 递归解法急速判断左右两边子树哪个depth最小,要注意如果有个节点只有一边孩子时,不能返回0,要返回另外一半边的depth. 递归解法:              …

题目: Given a binary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node. 题解: 递归解法:                                                            } 非递归解法,参考codegan…