104.二叉树的最大深度.java

import java.util.Queue;

/*
 * @lc app=leetcode.cn id=104 lang=java
 *
 * [104] 二叉树的最大深度
 */

// @lc code=start
/**
 * 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 depth = 0;
        Queue<TreeNode> que = new LinkedList<>();
        que.offer(root);
        while (!que.isEmpty()) {
            depth++;
            int length = que.size();
            for (int i = 0; i < length; i++) {
                TreeNode node = que.poll();
                if (node.left != null) {
                    que.offer(node.left);
                }
                if (node.right != null) {
                    que.offer(node.right);
                }
            }
        }
        return depth;
    }
}
// @lc code=end