【leetcode 二叉树平衡判断】

1、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.

平衡二叉树的定义：每个节点的左右子树的高度差不超过1

2、分析

用递归法
 一棵树平衡的条件：左子树平衡&&右子树平衡&&左右子树高度差不超过1

3、代码

<span style="font-size:18px;">/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
 /*递归法
 一棵树平衡的条件：左子树平衡&&右子树平衡&&左右子树高度差不超过1
 */
class Solution {
public:
    bool isBalanced(TreeNode *root) {
        if(!root) return true;
        return isBalanced(root->left) && isBalanced(root->right) && abs(treeDepth(root->left)-treeDepth(root->right))<2 ;
    }
private:
   int treeDepth(TreeNode *root)  //求树的高度 又是递归
   {
       if(!root) return 0;
       return max(treeDepth(root->left),treeDepth(root->right))+1;
   }
};</span>