/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        if(!root) return true;
        int plus=abs(depth(root->left)-depth(root->right));//当前结点的左右子树高度差
        return (plus<=1)&&(isBalanced(root->left)&&(isBalanced(root->right)));
    }
    //求解二叉树的高度
    int depth(TreeNode* node){
        if(node==NULL) return 0;
        return max(depth(node->left),depth(node->right))+1;
    }
};