《剑指offer》刷题笔记（知识迁移能力）：平衡二叉树

---

• 转载请注明作者和出处：http://blog.csdn.net/u011475210
• 代码地址：https://github.com/WordZzzz/Note/tree/master/AtOffer
• 刷题平台：https://www.nowcoder.com/
• 题  库：剑指offer
• 编  者：WordZzzz

---

题目描述

输入一棵二叉树，判断该二叉树是否是平衡二叉树。

解题思路

可以在之前求二叉树深度的基础上进行算法实现，但是需要多次遍历。我们也可以用后序遍历，这样我们只需要遍历一次即可，需要需要存储一下左右子树的深度。

C++版代码实现

多次遍历

class Solution {public:    bool IsBalanced_Solution(TreeNode* pRoot) {        if(pRoot == NULL)            return true;        int left = getDepth(pRoot->left);        int right = getDepth(pRoot->right);        int diff = left - right;        if(diff > 1 || diff < -1)            return false;        return IsBalanced_Solution(pRoot->left) && IsBalanced_Solution(pRoot->right);    }    int getDepth(TreeNode* pRoot){        return pRoot ? max(getDepth(pRoot->left),getDepth(pRoot->right))+1 :0;    }};

一次遍历

class Solution {public:    bool IsBalanced_Solution(TreeNode* pRoot) {        int depth = 0;        return IsBalanced(pRoot, &depth);    }    int IsBalanced(TreeNode* pRoot, int* depth){        if(pRoot == NULL){            *depth = 0;            return true;        }        int left, right;        if(IsBalanced(pRoot->left, &left) && IsBalanced(pRoot->right, &right)){            int diff = left - right;            if(diff <= 1 && diff >= -1){                *depth = 1 + (left > right ? left : right);                return true;            }        }        return false;    }};

Python版代码实现

多次遍历

# -*- coding:utf-8 -*-# class TreeNode:#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution:    def IsBalanced_Solution(self, pRoot):        # write code here        if pRoot == None:            return True        left = self.getDepth(pRoot.left)        right = self.getDepth(pRoot.right)        diff = abs(left - right)        if diff > 1:            return False        return self.IsBalanced_Solution(pRoot.left) and self.IsBalanced_Solution(pRoot.right)    def getDepth(self, pRoot):        if not pRoot:            return 0        return max(self.getDepth(pRoot.left),self.getDepth(pRoot.right))+1

系列教程持续发布中，欢迎订阅、关注、收藏、评论、点赞哦～～(￣▽￣～)～

完的汪(∪｡∪)｡｡｡zzz