/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    
    int getHeight(TreeNode *root){
        if(root==NULL)return 0;
        
        //获得左子树高度
        int leftHeight=getHeight(root->left);
        if(leftHeight==-1)return -1;
        //获得右子树高度
        int rightHeight=getHeight(root->right);
        if(rightHeight==-1)return -1;
        
        //判断左右子树高度差是否符合要求, 如果符合要求，则返回当前二叉树的高，如果不符合要求，则返回-1
        if(abs(leftHeight-rightHeight)<=1) 
            return max(leftHeight, rightHeight)+1;
        
        return -1;
    }

    bool isBalanced(TreeNode *root) {
        if(root==NULL)return true;
        
        int height=getHeight(root);
        if(height==-1)return false;
        return true;
        
    }
};