A Knight's Tour

[danthegreat]

An old guy named Euler proposed a problem regarding the movemesnt of knight chess pieces on a chess board. Euler proposed the challenge of putting the knight piece on every square of an empty chessboard (aka a matrix) and to touch all 100 squares once and only once..

I need help with my program. I have tried printing variables but I cannot keep track of how the array index could possibly be going out of bounds. Anyone know? Here's mah code!

/* 
 * Program that moves a "knight" around an empty chessboard to touch each of the squares once and only once. 
 */
import java.util.*;
public class Ansher_knighttour 
{
    public static void main(String[] args)
    {
        Scanner keyboard = new Scanner(System.in);
        Random randGen = new Random();
        
        int[][] matrix = new int[10][10];
        int[] possibleMoves;
        int row_start;
        int col_start;
        int random;
        int counter=0;
        int move;
        


        
        System.out.print("Enter row # to start: ");
        row_start=keyboard.nextInt();
        
        System.out.print("Enter column # to start: ");
        col_start=keyboard.nextInt();
        
        matrix[row_start][col_start]='K';
         
        
        int counte;
        int counte_track=0;
        
        do
        {
        int[] vertical={row_start+1,row_start+2, row_start+2, row_start+1, row_start-1, row_start-2, row_start -2, row_start-1};
        int[] horizontal={col_start-2, col_start-1, col_start+1, col_start+2, col_start+2, col_start+1, col_start-1,col_start-2};
    
        
        
        possibleMoves=possibleMoves(row_start, col_start, matrix, vertical, horizontal);
        counte=possibleMoves.length;
        random=randGen.nextInt(possibleMoves.length)+1;
        counter++;
        
        move=possibleMoves[random];
        counte_track++;
        
        System.out.println(move);
        
[B]        row_start=vertical[move];
        col_start=horizontal[move];[/B]


        matrix[row_start][col_start]=counter;        
        
        }while(counte!=counte_track);
        
        
        displayResults(matrix);


        
        
    }


    




    public static void displayResults(int [][] matrix)
    {
        int curMax=Integer.MIN_VALUE;
        
        System.out.print("    ");
        for(int i3=1; i3<=matrix.length; i3++)
        {
            System.out.print(i3 + "   ");
        }
        
        System.out.println("");
        for(int i=0; i<matrix.length; i++)
        {


            System.out.print(i+1);
            for(int i2=0; i2<matrix[i].length; i2++)
            {
                if(matrix[i][i2]>curMax)
                {
                    curMax=matrix[i][i2];
                }
                if(matrix[i][i2]>=0 && matrix[i][i2]<=9)
                {
                    System.out.print("   " + matrix[i][i2]);
                }
                else
                {
                System.out.print("  " + matrix[i][i2]);
                }
            }
            System.out.println("");
        }
        
        
        
        System.out.println(curMax + " squares were visited.");
        
    }


    


    public static int[] possibleMoves(int row, int col, int[][] matrix, int[] vertical, int[]horizontal)
    {


        int[] possibleMoves=new int[9];
        
        
        for(int i=0; i<vertical.length;i++)
        {
            if(vertical[i]>=0 && vertical[i]<matrix.length || horizontal[i]>=0 && horizontal[i]<matrix.length)
            {
                possibleMoves[i]=vertical[i];
                                
            }
            else
            {
                possibleMoves[i]=-1;
            }
        }
        
        int counter=0;
        
        for(int i2=0; i2<possibleMoves.length; i2++)
        {
            if(possibleMoves[i2]>0)
            {
                counter++;
            }
        }
        
        int[] possibleMovesFINAL=new int[counter];


        int counter2=-1;
        
        for(int i3=0; i3<possibleMoves.length; i3++)
        {
            if(possibleMoves[i3]>0)
            {
                
                
                counter2++;
                possibleMovesFINAL[counter2]=possibleMoves[i3];
            }
        }
        
        
        


        return possibleMovesFINAL;
        


        
        
        
        
        
        
    }


}

Bolded is where my problem is. Also, I don't know how to keep track of where I have already been.

[danthegreat]

Ok i tried this variation

/*  * Program that moves a "knight" around an empty chessboard to touch each of the squares once and only once. 
 */
import java.util.*;
public class Ansher_knighttour 
{
	public static void main(String[] args)
	{
		Scanner keyboard = new Scanner(System.in);
		Random randGen = new Random();
		
		int[][] matrix = new int[10][10];
		int[] possibleMoves;
		int row_start;
		int col_start;
		int random;
		int counter=0;
		int move;
		


		
		System.out.print("Enter row # to start: ");
		row_start=keyboard.nextInt();
		
		System.out.print("Enter column # to start: ");
		col_start=keyboard.nextInt();
		
		matrix[row_start][col_start]='K';
		//Loop should start here.
		


		int num=0;
		
		do
		{
		int[] vertical={row_start+1,row_start+2, row_start+2, row_start+1, row_start-1, row_start-2, row_start -2, row_start-1};
		int[] horizontal={col_start-2, col_start-1, col_start+1, col_start+2, col_start+2, col_start+1, col_start-1,col_start-2};
	
		
		
		possibleMoves=possibleMoves(row_start, col_start, matrix, vertical, horizontal);


[B]		random=randGen.nextInt(possibleMoves.length);[/B]
[B]	[/B]
[B]		System.out.println(possibleMoves[random]);[/B]
[B]		[/B]
[B]		if(possibleMoves[random]!=-1)[/B]
[B]		{[/B]
[B]			counter++;[/B]
[B]			move=possibleMoves[random];[/B]
[B]			possibleMoves[random]=-1;[/B]
[B]		[/B]
[B]			row_start=vertical[move];[/B]
[B]			col_start=horizontal[move];[/B]
[B]			matrix[row_start][col_start]=counter;		[/B]
[B]		}[/B]
[B]		else[/B]
[B]		{[/B]
[B]			num++;[/B]
[B]		}[/B]
[B]		[/B]
[B]		}while(counter<=100 || num!=possibleMoves.length);[/B]


		
		displayResults(matrix);


		
		
	}


	




	public static void displayResults(int [][] matrix)
	{
		int curMax=Integer.MIN_VALUE;
		
		System.out.print("    ");
		for(int i3=1; i3<=matrix.length; i3++)
		{
			System.out.print(i3 + "   ");
		}
		
		System.out.println("");
		for(int i=0; i<matrix.length; i++)
		{


			System.out.print(i+1);
			for(int i2=0; i2<matrix[i].length; i2++)
			{
				if(matrix[i][i2]>curMax)
				{
					curMax=matrix[i][i2];
				}
				if(matrix[i][i2]>=0 && matrix[i][i2]<=9)
				{
					System.out.print("   " + matrix[i][i2]);
				}
				else
				{
				System.out.print("  " + matrix[i][i2]);
				}
			}
			System.out.println("");
		}
		
		
		
		System.out.println(curMax + " squares were visited.");
		
	}


	


	public static int[] possibleMoves(int row, int col, int[][] matrix, int[] vertical, int[]horizontal)
	{


		int[] possibleMoves=new int[9];
		
		
		for(int i=0; i<vertical.length;i++)
		{
			if(vertical[i]>=0 && vertical[i]<matrix.length || horizontal[i]>=0 && horizontal[i]<matrix.length)
			{
				possibleMoves[i]=vertical[i];
								
			}
			else
			{
				possibleMoves[i]=-1;
			}
		}
		
		int counter=0;
		
		for(int i2=0; i2<possibleMoves.length; i2++)
		{
			if(possibleMoves[i2]>0)
			{
				counter++;
			}
		}
		
		int[] possibleMovesFINAL=new int[counter];


		int counter2=-1;
		
		for(int i3=0; i3<possibleMoves.length; i3++)
		{
			if(possibleMoves[i3]>0)
			{
				
				
				counter2++;
				possibleMovesFINAL[counter2]=possibleMoves[i3];
			}
		}
		
		
		


		return possibleMovesFINAL;
		


		
		
		
		
		
		
	}


}

this is what happens with output:
Enter row # to start: 3
Enter column # to start: 3
2
4
2
4
6
1
4
6
4
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10
at Ansher_knighttour.main(Ansher_knighttour.java:58)

for some reason it doesn't it never reaches the end of the loop. sigh.