LeetCode -- Balanced Binary Tree

题目描述：


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.


就是判断一棵树，是否为平衡树。


平衡树的定义就是，左右子树的高度差不能超过1。


思路：


判断每个节点是否平衡 
对于任何一个节点，判断左右是否平衡。仅当左右子树都平衡时，当前树才算平衡。
分别求出左右子树的高度，返回Math.Max(左子树高度，右子树高度)+1




实现代码：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public bool IsBalanced(TreeNode root) 
    {
        if(root == null || root.left == null && root.right == null){
    		return true;
    	}
    	
    	var l = Depth(root.left);
    	var r = Depth(root.right);
    	if(Math.Abs(l-r) > 1){
    		return false;
    	}
    	
    	var bLeft = IsBalanced(root.left);
    	var bRight = IsBalanced(root.right);
    	return bLeft && bRight;
    }
	


    public int Depth(TreeNode node)
    {
        if(node == null){
        	return 0;
        }
        
        var l = Depth(node.left);
        var r = Depth(node.right);
        var len = Math.Max(l,r);
	    return len + 1;
    }


}