《leetCode》：Balanced Binary Tree

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.

思路

#include<stdio.h>
#include<stdlib.h>

/**
* Definition for a binary tree node.*/
struct TreeNode {
int val;
struct TreeNode *left;
struct TreeNode *right;
};
//思路：从上到下开始遍历，判断是否存在高度差大于1. 转化为求每个节点的最大深度
int max(int a,int b){
return (a>=b)?a:b;
}
int nodeDepth(struct TreeNode* root){
if(root==NULL){
return 0;
}
//当前节点的左右子树的高度
int leftSubNodeDepth=nodeDepth(root->left);
int rightSubNodeDepth=nodeDepth(root->right);
return max(leftSubNodeDepth,rightSubNodeDepth)+1;
}
bool isBalancedHelper(struct TreeNode* root){
if(root==NULL){
return true;
}
//先判断当前节点是否为高度平衡的
int dif=nodeDepth(root->left)-nodeDepth(root->right);
if(dif>1||dif<-1){//注意是绝对值大于1 就返回false
return false;
}
//继续判断当前节点的左右子节点是否是高度平衡的
return isBalancedHelper(root->left)&&isBalancedHelper(root->right);
}
bool isBalanced(struct TreeNode* root) {
if(root==NULL){
return true;
}
return isBalancedHelper(root);

}