leetcode 559. Maximum Depth of N-ary Tree

Seawolf

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].

/*
// 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 {
    
    int max;
    public int maxDepth(Node root) {
        if(root == null) return 0;
        
        int dep = 1;
        dfs(root,dep);
        return max;
    }
    
    public void dfs(Node root, int depth){
        if(depth > max) max = depth;
        if(root.children.size() == 0) return;
        int len = root.children.size();
        
        for(int i = 0; i< len; i++){
            if(root.children.get(i) != null){
                dfs(root.children.get(i), depth+1);
            }
        }
    }
}