559. N 叉树的最大深度

给定一个 N 叉树，找到其最大深度。

最大深度是指从根节点到最远叶子节点的最长路径上的节点总数。

输入：root = [1,null,3,2,4,null,5,6]
输出：3

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> children;

    public Node() {}

    public Node(int _val) {
        val = _val;
    }

    public Node(int _val, List<Node> _children) {
        val = _val;
        children = _children;
    }
};
*/

class Solution {
    public int maxDepth(Node root) {
        if (root == null) {
            return 0;
        }
        int maxChildDepth = 0;
        List<Node> children = root.children;
        for (Node child : children) {
            int childDepth = maxDepth(child);
            maxChildDepth = Math.max(maxChildDepth, childDepth);
        }
        return maxChildDepth + 1;
    }
}

class Solution {
    public int maxDepth(Node root) {
        if (root == null) {
            return 0;
        }
        Queue<Node> queue = new LinkedList<Node>();
        queue.offer(root);
        int ans = 0;
        while (!queue.isEmpty()) {
            int size = queue.size();
            while (size > 0) {
                Node node = queue.poll();
                List<Node> children = node.children;
                for (Node child : children) {
                    queue.offer(child);
                }
                --size;
            }
            ++ans;
        }
        return ans;
    }
}