559. Maximum Depth of N-ary Tree

Given a n-ary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Nary-Tree input serialization is represented in their level order traversal, each group of children is separated by the null value (See examples).

Example 1:

Input: root = [1,null,3,2,4,null,5,6]
Output: 3

Example 2:

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

Constraints:

• The depth of the n-ary tree is less than or equal to 1000.
• The total number of nodes is between [0, 10^4].

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

        Queue<Node> queue = new LinkedList<>();
        queue.offer(root);

        int depth = 0;

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

            for(int i = 0; i < size; i++)
            {
                Node current = queue.poll();
                for(Node child: current.children) queue.offer(child);
            }

            depth++;
        }

        return depth;
    }
}

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

 模仿普通的二叉树，改写成

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

        int max = 0;
        for (Node child : root.children) { //replace left&right to for loop
            int value = maxDepth(child);
            
            if (value > max) {
                max = value;
            }
        }
        return max +1;
    }
}