N 叉树的直径

/*
 * Leetcode 1522: Diameter of N-ary Tree (Java Stream)
 * 
 * Problem Statement: Given an N-ary tree, find the length of the diameter. 
 * The diameter of an N-ary tree is the longest path between any two nodes, 
 * which may or may not pass through the root.
 * 
 * Approach:
 * 1. Use a helper function to determine the depth of the tree recursively.
 * 2. For each node, use streams to calculate the depths of its children.
 * 3. Track the two largest depths to compute the diameter.
 * 4. Return the maximum diameter found.
 */

import java.util.Comparator;
import java.util.List;

class Solution {
    private int maxDiameter = 0;
    
    public int diameter(Node root) {
        if (root == null) return 0;
        depth(root);
        return maxDiameter;
    }
    
    private int depth(Node node) {
        if (node == null) return 0;
        List<Integer> depths = node.children.stream().map(this::depth).sorted(Comparator.reverseOrder()).toList();
        int max1 = depths.size() > 0 ? depths.get(0) : 0;
        int max2 = depths.size() > 1 ? depths.get(1) : 0;
        maxDiameter = Math.max(maxDiameter, max1 + max2);
        return max1 + 1;
    }
}