题解 | #判断是不是平衡二叉树#

判断是不是平衡二叉树 递归解法时间复杂度O(n) 空间复杂度O(h) h为二叉树高度，对于平衡二叉树为O(logn)
using System;
using System.Collections.Generic;

/*
public class TreeNode
{
	public int val;
	public TreeNode left;
	public TreeNode right;

	public TreeNode (int x)
	{
		val = x;
	}
}
*/

class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param pRoot TreeNode类 
     * @return bool布尔型
     */
    public bool IsBalanced_Solution (TreeNode pRoot) {
        // write code here
        return checkHeight(pRoot) != -1;
    }

    public int checkHeight(TreeNode node) {
        if(node == null){
            return 0;
        }

        int leftHeight = checkHeight(node.left);
        if(leftHeight == -1){
            return -1;
        }
        int rightHeight = checkHeight(node.right);
        if(rightHeight == -1){
            return -1;
        }

        if(Math.Abs(leftHeight - rightHeight) > 1){
            return -1;
        }

        return Math.Max(leftHeight, rightHeight) + 1;
    }
}