559. Maximum Depth of N-ary Tree

Problem

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 total number of nodes is in the range [0, 10^4].

• The depth of the n-ary tree is less than or equal to 1000.

Solution (Java)

/*
// 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 {
    private int max = 0;

    public int maxDepth(Node root) {
        if (root == null) {
            return 0;
        }
        if (root.children == null || root.children.isEmpty()) {
            return 1;
        }
        for (Node child : root.children) {
            findDepth(child, 1);
        }
        return max;
    }

    private void findDepth(Node n, int d) {
        if (n.children != null && !n.children.isEmpty()) {
            for (Node no : n.children) {
                findDepth(no, d + 1);
            }
        } else {
            max = Math.max(max, d + 1);
        }
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).