《剑指offer》刷题笔记（知识迁移能力）：平衡二叉树

淡淡的烟草味﹌ 2022-06-03 00:20 56阅读 0赞

# 《剑指offer》刷题笔记（知识迁移能力）：平衡二叉树 #

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*  **转载请注明作者和出处：[http://blog.csdn.net/u011475210][http_blog.csdn.net_u011475210]**
 *  **代码地址：[https://github.com/WordZzzz/Note/tree/master/AtOffer][https_github.com_WordZzzz_Note_tree_master_AtOffer]**
 *  **刷题平台：[https://www.nowcoder.com/][https_www.nowcoder.com]**
 *  **题  库：剑指offer**
 *  **编  者：WordZzzz**

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*  剑指offer刷题笔记知识迁移能力平衡二叉树
    
     *  题目描述
     *  解题思路
     *  C版代码实现
        
         *  多次遍历
         *  一次遍历
     *  Python版代码实现
        
         *  多次遍历

## 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 = None
    class 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

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[http_blog.csdn.net_u011475210]: http://blog.csdn.net/u011475210
[https_github.com_WordZzzz_Note_tree_master_AtOffer]: https://github.com/WordZzzz/Note/tree/master/AtOffer
[https_www.nowcoder.com]: https://www.nowcoder.com/