Distance Code

import java.util.Scanner;
import java.util.ArrayList;

public class distance {

    public static class Node {
        ArrayList<Node> children;
        Node parent;
        int id;

        public Node(int id) {
            children = new ArrayList<>();
            this.id = id;
        }
    }

    public static void encode(Node root) {
        // remove nodes depth-first
        for (int i = 0; i < root.children.size(); i++) {
            encode(root.children.get(i));
        }
        System.out.println(root.id + 1);
    }

    public static int decode(int[] distances, Node[] nodes, int pIndex) {
        // loop through nodes that belong to parent
        int i = pIndex + 1;
        while (i < distances.length && distances[i] == 1 + distances[pIndex]) {
            nodes[pIndex].children.add(nodes[i]);
            System.out.println((nodes[i].id + 1) + " " + (nodes[pIndex].id + 1));
            i = decode(distances, nodes, i);
        }
        return i;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int t = Integer.parseInt(scanner.next());
        int n = Integer.parseInt(scanner.next());

        Node[] nodes = new Node[n];
        for (int i = 0; i < nodes.length; i++) {
            nodes[i] = new Node(i);
        }

        if (t == 1) { // encode
            for (int i = 0; i < n - 1; i++) {
                int a = Integer.parseInt(scanner.next());
                int b = Integer.parseInt(scanner.next());
                nodes[b - 1].children.add(nodes[a - 1]);
                nodes[a - 1].parent = nodes[b - 1];
            }
            Node root = nodes[0];
            while (root.parent != null) {
                root = root.parent;
            }
            encode(root);
        } else { // decode
            // get distances
            int[] distances = new int[n + 1]; // add 0 as last element
            for (int i = 0; i < n - 1; i++) {
                distances[i + 1] = Integer.parseInt(scanner.next());
            }
            
            // run decode with index = n - 1
            decode(distances, nodes, 0);
        }

        scanner.close();
    }
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 3

Group: 1, 2, 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 5

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 6

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 7

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 8

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 9

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 10

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 11

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 12

Group: 2, 3

Verdict: WRONG ANSWER

Test 13

Group: 2, 3

Verdict: WRONG ANSWER

Test 14

Group: 2, 3

Verdict: WRONG ANSWER

Test 15

Group: 2, 3

Verdict: WRONG ANSWER

Test 16

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 17

Group: 3

Verdict: WRONG ANSWER

Test 18

Group: 3

Verdict: WRONG ANSWER

Test 19

Group: 3

Verdict: WRONG ANSWER

Test 20

Group: 1, 2, 3

Verdict: WRONG ANSWER