leetcode_110_Balanced Binary Tree

描述：

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.

思路：

走了好多弯路，最后才发现直接根据定义来就可以了，左右子树的深度不超过1且左右子树都是平衡二叉树，就是这么简洁明快。

代码：

/**
 * Definition for binary tree
 * 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;
		if(root.left==null&&root.right==null)
			return true;
		int len=maxDepth(root.left)-maxDepth(root.right);
		if(Math.abs(len)<=1&&isBalanced(root.left)&&isBalanced(root.right))
			return true;
		return false;
    }
	public int maxDepth(TreeNode root) {
        if(root==null)
        	return 0;
        if(root.left==null&&root.right==null)
        	return 1;
        int num1=maxDepth(root.left),num2=maxDepth(root.right);
        int num=(num1>=num2?num1:num2)+1;
        return num;
    }
}

结果：