LeetCode 110. Balanced Binary Tree 递归求解

Posted 2020-06-16 bruce128

   题目链接：https://leetcode.com/problems/balanced-binary-tree/ 

110. Balanced Binary Tree

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Total Accepted: 97926 Total Submissions: 292400 Difficulty: Easy

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.

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    判断一棵树是否是平衡二叉树。BST的递归定义：当一棵树的左右两棵子树的高度只差不超过1，那么该树是平衡二叉树。

    用后根遍历求解。先计算两棵子树的高度差。

    我的AC代码

public class BalancedBinaryTree {
	static boolean ok = true;
	
	public static void main(String[] args) {
		TreeNode n1 = new TreeNode(1);
		TreeNode n2 = new TreeNode(2);
		n1.left = n2;
		System.out.println(isBalanced(n1));
	}

	public static boolean isBalanced(TreeNode root) {
        ok = true;
        dfs(root);
        return ok;
    }
	
	public static int dfs(TreeNode root) {
		if(root == null || !ok) return 0;
		int ha = dfs(root.left);
		int hb = dfs(root.right);
		
		if(Math.abs(ha - hb) > 1) ok = false;
		return Math.max(ha, hb) + 1;
	}
}