[LeetCode] 110. Balanced Binary Tree Java

题目：

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

题意及分析：给出一课二叉树，判断是否是二叉平衡树。使用递归，分别求出左右子树的高度，然后相减，看是否符合条件，若符合，则分别判断左右子节点是否符合。

代码：

/**
 * Definition for a binary tree node.
 * public 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 = count(root.left);
        int right =count(root.right);
        return Math.abs(left - right) <= 1 && isBalanced(root.left) && isBalanced(root.right);
    }

    public int count(TreeNode node){        //求一棵树的高度,为左右子树的最大高度+1
        if(node==null) return 0;
        return Math.max(count(node.left),count(node.right))+1;
    }
}