[LeetCode 104] Maximum Depth of Binary Tree

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Description

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Given the root of a binary tree, return its maximum depth.

A binary tree’s maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Example 1

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

Example 2

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

Constraints

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• The number of nodes in the tree is in the range [0, 104].
• -100 <= Node.val <= 100

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 int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int l = maxDepth(root.left);
        int r = maxDepth(root.right);
        return 1 + Math.max(l, r);
    }
}

Runtime	Memory
0 ms	43.4 MB

다른 풀이

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class Solution {
    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }

        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        int depth = 0;

        while (!queue.isEmpty()) {
            depth++;
            int levelSize = queue.size();

            for (int i = 0; i < levelSize; i++) {
                TreeNode node = queue.poll();
                if (node.left != null) {
                    queue.add(node.left);
                }
                if (node.right != null) {
                    queue.add(node.right);
                }
            }
        }

        return depth;        
    }
}

Reference

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• https://github.com/doocs/leetcode/blob/main/solution/0100-0199/0104.Maximum%20Depth%20of%20Binary%20Tree/Solution.java