1const classifyNodes = (nodes) => {
2    const childCount = {};
3    const types = {};
4
5    nodes.forEach(([id, p_id]) => {
6        if (p_id !== null) {
7            if (!childCount[p_id]) childCount[p_id] = 0;
8            childCount[p_id]++;
9        }
10        types[id] = "Leaf";
11    });
12
13    nodes.forEach(([id, p_id]) => {
14        if (p_id === null) {
15            types[id] = "Root";
16        } else if (childCount[id]) {
17            types[id] = "Inner";
18        }
19    });
20
21    for (const id in types) {
22        console.log(id, types[id]);
23    }
24};
25
26const nodes = [[1, null], [2, 1], [3, 1], [4, 2], [5, 2]];
27classifyNodes(nodes);

using System.Collections.Generic;

public class Node {
    public int Id, PId;
    public Node(int id, int pId) { Id = id; PId = pId; }
}

public class TreeNode {
    public static void ClassifyNodes(List<Node> nodes) {
        var isChild = new HashSet<int>();

        foreach (var node in nodes) {
            if (node.PId != -1) isChild.Add(node.PId);
        }

        foreach (var node in nodes) {
            if (node.PId == -1) {
                Console.WriteLine(node.Id + " Root");
            } else if (isChild.Contains(node.Id)) {
                Console.WriteLine(node.Id + " Inner");
            } else {
                Console.WriteLine(node.Id + " Leaf");
            }
        }
    }

    public static void Main() {
        List<Node> nodes = new List<Node> {
            new Node(1, -1), new Node(2, 1), new Node(3, 1), new Node(4, 2), new Node(5, 2)
        };
        ClassifyNodes(nodes);
    }
}