《剑指offer》刷题笔记（知识迁移能力）：平衡二叉树

《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

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