/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private int dfsHeight(TreeNode root){
        if(root==null)return 0;
        int leftHeight=dfsHeight(root.left);
        if(leftHeight==-1)return -1;
        int rightHeight=dfsHeight(root.right);
        if(rightHeight==-1)return -1;
        if(Math.abs(leftHeight-rightHeight)>1)return -1;
        return leftHeight>rightHeight?(leftHeight+1):(rightHeight+1);
    }
    public boolean isBalanced(TreeNode root) {
        int a=dfsHeight(root);
        if(a==-1)return false;
        return true;
    }
}