判斷一棵樹是否爲平衡樹

import java.util.*;
public class Balance {
    public boolean isBalance(TreeNode root) {
      if(root==null){
          return true;
      }
        if(Math.abs(depth(root.left)-depth(root.right))>1){
            return false;
        }
       else{
           return isBalance(root.left)&isBalance(root.right);
       }
            
        }
    public int depth(TreeNode root){
        if(root==null){
            return 0;
        }else{
            return Math.max(depth(root.left),depth(root.right))+1;
        }
    }
    }