Maximum Depth of N-ary Tree

Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: 5

思路1：DFS ，divide and conquer

/*
// 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 depth = 0;
        for(Node child: root.children) {
            depth = Math.max(depth, maxDepth(child));
        }
        return depth + 1;
    }
}

思路2：BFS level order

/*
// 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;
        }
        Queue<Node> queue = new LinkedList<Node>();
        queue.offer(root);
        int depth = 0;
        
        while(!queue.isEmpty()) {
            int size = queue.size();
            for(int i = 0; i < size; i++) {
                Node node = queue.poll();
                for(Node child: node.children) {
                    queue.offer(child);
                }
            }
            depth++;
        }
        return depth;
    }
}