LeetCode 110. Balanced Binary Tree

Question

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.

Explanation

在这里还是用递归，判断条件为1. 左右子树均balance 2.左右子树高度只差不超过1. 所以在这道题中，为了能返回两个值，就创建了一个新的类：ResultType。如果用python写就不用了。

Code

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */

class ResultType {
    public boolean isBalanced;
    public int maxDepth;
    public ResultType(boolean isBalanced, int maxDepth) {
        this.isBalanced = isBalanced;
        this.maxDepth = maxDepth;
    }
}

public class Solution {
    public boolean isBalanced(TreeNode root) {
        if (root == null) return true;
        return helper(root).isBalanced;
    }

    public ResultType helper(TreeNode root) {
        if (root == null ) return new ResultType(true, 0);
        ResultType left = helper(root.left);
        ResultType right = helper(root.right);
        if (left.isBalanced && right.isBalanced && Math.abs(left.maxDepth-right.maxDepth)<=1)  {
            return new ResultType(true, Math.max(left.maxDepth,right.maxDepth)+1);
        }
        return new ResultType(false, -1);
    }
}