I’ve been working on a school project and can not figure out the problem. The problem that the knight jumps back where it was in the the last step when a dead end occurs.
I’ve added the output for a 4×4 test and you can clarly see that the knight jumps back to turn number 11 when it sees that there’s a dead-way from number 12. It then continues from turn number 11 and “solves the tour”.
Also I’m unsure how to continue if a pattern don’t solve the problem. Because then I need to somehow log that pattern so that I don’t go in the same pattern all over again. Sorry for my bad Engligh and thanks in advance.
package knightsTour;
import java.util.Scanner;
import java.util.ArrayList;
public class KnightsTour
{
private static int turns = 0;
private static ArrayList<String> moves = new ArrayList<String>();
private static int squares;
private static int table[][];
private static boolean takeTour(int x, int y) {
// Checks if all squares is used. If true, algorithm will stop
if (checkIfFinished())
return true;
table[x][y] = ++turns;
// 2 Left, 1 Down
if (x > 1 && y < squares -1 && table[x-2][y+1] == 0)
{
moves.add("X: " + x + ", Y: " + y + ". Moving 2 Left, 1 Down");
if (takeTour(x-2, y+1))
{
return true;
}
}
// 2 Left, 1 Up
if (x > 1 && y > 0 && table[x-2][y-1] == 0)
{
moves.add("X: " + x + ", Y: " + y + ". Moving 2 Left, 1 Up");
if (takeTour(x-2, y-1))
{
return true;
}
}
// 2 Up, 1 Left
if (y > 1 && x > 0 && table[x-1][y-2] == 0)
{
moves.add("X: " + x + ", Y: " + y + ". Moving 2 Up, 1 Left");
if (takeTour(x-1, y-2))
{
return true;
}
}
// 2 Up, 1 Right
if (y > 1 && x < squares -1 && table[x+1][y-2] == 0)
{
moves.add("X: " + x + ", Y: " + y + ". Moving 2 Up, 1 Right");
if (takeTour(x+1, y-2))
{
return true;
}
}
// 2 Right, 1 Up
if (x < squares -2 && y > 0 && table[x+2][y-1] == 0)
{
System.out.println("x:" + x + ", y:" + y + " (2r,1u)moving to x:" + (x+2) + ", y:" + (y-1));
moves.add("X: " + x + ", Y: " + y + ". Moving 2 Right, 1 Up");
if (takeTour(x+2, y-1))
{
return true;
}
}
// 2 Right, 1 Down
if (x < squares -2 && y < squares -1 && table[x+2][y+1] == 0)
{
System.out.println("x:" + x + ", y:" + y + " (2r,1d)moving to x:" + (x+2) + ", y:" + (y+1));
moves.add("X: " + x + ", Y: " + y + ". Moving 2 Right, 1 Down");
if (takeTour(x+2, y+1))
{
return true;
}
}
// 2 Down, 1 Right
if (y < squares -2 && x < squares-1 && table[x+1][y+2] == 0)
{
moves.add("X: " + x + ", Y: " + y + ". Moving 2 Down, 1 Right");
if (takeTour(x+1, y+2))
{
return true;
}
}
// 2 Down, 1 Left
if (y < squares -2 && x > 0 && table[x-1][y+2] == 0)
{
moves.add("X: " + x + ", Y: " + y + ". Moving 2 Down, 1 Left");
if (takeTour(x-1, y+2))
{
return true;
}
}
return false;
}
// Checks if all squares is used
private static boolean checkIfFinished()
{
for (int i = 0; i < squares; i++)
{
for (int j = 0; j < squares; j++)
{
if (table[i][j] == 0)
return false;
}
}
return true;
}
// Made this to save code from 3 duplicates
private static void invalidNumber()
{
System.out.println("Invalid number! Killing proccess");
System.exit(0);
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Number of squares: ");
squares = Integer.parseInt(sc.nextLine());
if (squares < 1 )
invalidNumber();
System.out.println("Note: Start values is from 0 -> n-1"
+ "n0,0 is at top left side");
System.out.print("X start value: ");
int x = Integer.parseInt(sc.nextLine());
if (x < 0 || x > squares -1)
invalidNumber();
System.out.print("Y start value: ");
int y = Integer.parseInt(sc.nextLine());
if (y < 0 || y > squares -1)
invalidNumber();
sc.close();
table = new int[squares][squares];
boolean tourComplete = takeTour(x, y);
for (String s : moves)
{
System.out.println(s);
}
if (!tourComplete)
System.out.println("Did not find any way to complete Knights Tour!");
// Print the table with the move-numbers
for (int i = 0; i < squares; i++)
{
for (int j = 0; j < squares; j++)
{
System.out.printf("%4d", table[j][i]);
}
System.out.println();
}
}
}
Here’s the output for a 4×4:
Number of squares: 4 Note: Start values is from 0 -> n-1 0,0 is at top left side X start value: 0 Y start value: 0 x:0, y:0 (2r,1d)moving to x:2, y:1 x:1, y:0 (2r,1d)moving to x:3, y:1 x:0, y:1 (2r,1d)moving to x:2, y:2 x:1, y:1 (2r,1u)moving to x:3, y:0 x:1, y:1 (2r,1d)moving to x:3, y:2 x:1, y:2 (2r,1d)moving to x:3, y:3 X: 0, Y: 0. Moving 2 Right, 1 Down X: 2, Y: 1. Moving 2 Left, 1 Down X: 0, Y: 2. Moving 2 Up, 1 Right X: 1, Y: 0. Moving 2 Right, 1 Down X: 3, Y: 1. Moving 2 Left, 1 Down X: 1, Y: 2. Moving 2 Up, 1 Right X: 2, Y: 0. Moving 2 Left, 1 Down X: 0, Y: 1. Moving 2 Right, 1 Down X: 2, Y: 2. Moving 2 Left, 1 Down X: 0, Y: 3. Moving 2 Up, 1 Right X: 1, Y: 1. Moving 2 Right, 1 Up X: 1, Y: 1. Moving 2 Right, 1 Down X: 3, Y: 2. Moving 2 Left, 1 Down X: 1, Y: 1. Moving 2 Down, 1 Right X: 1, Y: 2. Moving 2 Right, 1 Down Did not find any way to complete Knights Tour! 1 4 7 12 8 11 2 5 3 6 9 13 10 14 15 16
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Answer
I figured out the problem! I had to put else blocks in every 8th if(takeTour(x+-a, y+-b)) statements inside the takeTour(int x, int y), and then return false. Now I just wonder how I will be able to track the pattern so that I can go back one step and try a new one