[LeetCode 110] Balanced Binary Tree

문제 바로가기

Description

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Given a binary tree, determine if it is height-balanced.

Example 1

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• Input: root = [3,9,20,null,null,15,7]
• Output: true

Example 2

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• Input: root = [1,2,2,3,3,null,null,4,4]
• Output: false

Example 3

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• Input: root = []
• Output: true

Constraints

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• The number of nodes in the tree is in the range [0, 5000].
• -10^4 <= Node.val <= 10^4

Code

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내 제출

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isBalanced(TreeNode root) {
                return height(root) >= 0;
    }

        private int height(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int l = height(root.left);
        int r = height(root.right);
        if (l == -1 || r == -1 || Math.abs(l - r) > 1) {
            return -1;
        }
        return 1 + Math.max(l, r);
    }
}

Runtime	Memory
0 ms	44.9 MB

다른 풀이

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isBalanced(TreeNode root) {
        if (root == null) {
            return true;
        }

        int leftDepth = getDepth(root.left);
        int rightDepth = getDepth(root.right);

        return (leftDepth - rightDepth <= 1 &&
            leftDepth - rightDepth >= -1) && 
            isBalanced(root.left) &&
            isBalanced(root.right);
    }

    private int getDepth (TreeNode node) {
        if (node == null) {
            return 0;
        }

        return 1 + Math.max(getDepth(node.left) ,getDepth(node.right));
    }
}

Reference

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• https://github.com/doocs/leetcode/blob/main/solution/0100-0199/0110.Balanced%20Binary%20Tree/Solution.java