leetcode_110

题目来源：https://leetcode.com/problems/balanced-binary-tree/

思路：递归。

代码：

/**

• Definition for a binary tree node.
• public class TreeNode {
• int val;
• TreeNode left;
• TreeNode right;
• TreeNode(int x) { val = x; }

• }
  */
  class Solution {

  boolean flag = true;

  public int dfs(TreeNode root){

  if (root == null){
      return 0;
  }
  if (flag == false){
      return -1;
  }
  int left = dfs(root.left);
  int right = dfs(root.right);
  if(Math.abs(left-right)>1){
      flag = false;
  }
  return Math.max(left,right)+1;
  

  }

  public boolean isBalanced(TreeNode root) {

  dfs(root);
  return flag;
  

  }
  }