class TreeNode {

     int val;

     TreeNode left;

     TreeNode right;

     TreeNode(int x) { val = x; }

 }

public class Solution {

    public boolean isBalanced(TreeNode root) {

        if(root==null)return true;

        int left=treeDepth(root.left);

        int right=treeDepth(root.right);

        if(Math.abs(left-right)<=1){//条件

            if(isBalanced(root.left)&&isBalanced(root.right))//递归调用isBanlianced(root);

                return true;

        }

        return false;

    }

    private int treeDepth(TreeNode root) {//求树的深度

        // TODO Auto-generated method stub

        if(root==null)return 0;

        return Math.max(treeDepth(root.right), treeDepth(root.left))+1;

    }

}