Ratsun reitit

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

public class RatsunReitit {

    private static final Scanner scanner = new Scanner(System.in);
    private static int boardSize;
    private static Node[][] board;

    public static void main(String[] args) {

        boardSize = scanner.nextInt();
        scanner.nextLine();

        board = new Node[boardSize][boardSize];

        for(int i = 0; i < boardSize; i++) {
            for(int j = 0; j < boardSize; j++) {
                board[i][j] = new Node(i, j);
            }
        }

        board[0][0].distance = 0;
        ArrayList<Node> nodesToCheck = new ArrayList<Node>();
        nodesToCheck.add(board[0][0]);

        while(!allNodesHaveBeenFound()) {
            ArrayList<Node> nodesFound = new ArrayList<Node>();
            for(Node node : nodesToCheck) {
                node.findAdjacentNodes(nodesFound);
            }
            nodesToCheck = nodesFound;
        }
        
        String s = "";
        for(int i = 0; i < boardSize; i++) {
            for(int j = 0; j < boardSize; j++) {
                s += board[i][j].distance + " ";
            }
            s += "\n";
        }
        System.out.print(s);
    }

    private static boolean allNodesHaveBeenFound() {
        for(int i = 0; i < boardSize; i++) {
            for(int j = 0; j < boardSize; j++) {
                if(board[i][j].distance == -1)
                    return false;
            }
        }
        return true;
    }

    private static class Node {

        public int distance;
        private int[] coords;

        public Node(int x, int y) {
            coords = new int[] {x, y};
            distance = -1;
        }

        public void findAdjacentNodes(ArrayList<Node> foundNodes) {

            int[][] adjacentNodes = new int[][] {
                {coords[0]+1, coords[1]+2},
                {coords[0]+2, coords[1]+1},
                {coords[0]+2, coords[1]-1},
                {coords[0]+1, coords[1]-2},
                {coords[0]-1, coords[1]-2},
                {coords[0]-2, coords[1]-1},
                {coords[0]-2, coords[1]+1},
                {coords[0]-1, coords[1]+2}
            };

            for(int[] nodeCoords : adjacentNodes) {
                if(nodeCoords[0] >= 0 && nodeCoords[0] < boardSize && nodeCoords[1] >= 0 && nodeCoords[1] < boardSize) {
                    Node currentlyCheckedNode = board[nodeCoords[0]][nodeCoords[1]];
                    if(currentlyCheckedNode.distance == -1) {
                        currentlyCheckedNode.distance = this.distance + 1;
                        foundNodes.add(currentlyCheckedNode);
                    }
                }
            }
        }
    }
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 1, 2, 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: ACCEPTED

Test 5

Group: 1, 2, 3

Verdict: ACCEPTED

Test 6

Group: 1, 2, 3

Verdict: ACCEPTED

Test 7

Group: 1, 2, 3

Verdict: ACCEPTED

Test 8

Group: 2, 3

Verdict: ACCEPTED

Test 9

Group: 2, 3

Verdict: ACCEPTED

Test 10

Group: 2, 3

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED