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Thread: Recursive Solution to Knights tour

  1. #1
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    Default Recursive Solution to Knights tour

    When I run this program as it is I think the program ends up leaving me in a infinite loop of recursion. Basically this program is suppose to traverse a chess board in the way a knight moves, recursively. The recursive method traverse is support to backtrack each time the knight lands on a square that is not valid, off the board or in programming terms off the 2D array. Anyway as it is, like I said it doesn't work. I can't figure out what part of the recursive method should be tweaked and more importantly how it should be tweaked. So, if anyone who has done wrote this program before or is just a genius when it comes to recursive algorithms I really need some advice on where to go from now. If you could just point out where and how I should fix this method with some snippets of code to illustrate the problem, it would be great. Thanks.



    public class KnightTour {
     
    	static int[][]board = new int[8][8];
    	static int globalCount = 0;
     
    	public static void main(String[] args) {
    		init(board);
     
    		System.out.println(traverse(0,0,0));
     
    		System.out.println(globalCount);
    		print(board);
     
     
    	}
     
     
     
     
     
     
    	public static boolean traverse(int count, int ver, int hor){
    		//if we are in the proper bounds we can assign the value to the board
    	    if(count >= 64){
    	    	return true;
    	    }
    	    //up 2 left 1
    	    if(hor <= 7 && hor >=0 && ver >= 0 && ver <= 7){
    			board[ver][hor] = count;
    			traverse(count+1,ver-2, hor -1);
    		}
    	    //up 2 right 1
    		if(hor <= 7 && hor >=0 && ver >= 0 && ver <= 7){
    			board[ver][hor] = count;
    			traverse(count + 1, ver-2, hor+1);
    		}
    	    //down 2 right 1
    		if(hor <= 7 && hor >=0 && ver >= 0 && ver <= 7){
    			board[ver][hor] = count;
    			traverse(count + 1, ver+2, hor+1);
    		}
    		//down 2 left 1
    		if(hor <= 7 && hor >=0 && ver >= 0 && ver <= 7){
    			board[ver][hor] = count;
    			traverse(count + 1, ver+2, hor-1);
    		}
    	    //left 2 down 1
    		if(hor <= 7 && hor >=0 && ver >= 0 && ver <= 7){
    			board[ver][hor] = count;
    			traverse(count + 1, ver+1, hor-2);
    		}
    	    //left 2 up 1
    		if(hor <= 7 && hor >=0 && ver >= 0 && ver <= 7){
    			board[ver][hor] = count;
    			traverse(count + 1, ver-1, hor-2);
    		}
    	    //right 2 down 1
    		if(hor <= 7 && hor >=0 && ver >= 0 && ver <= 7){
    			board[ver][hor] = count;
    			traverse(count + 1, ver+1, hor+2);
    		}
    		//right 2 up 1
    		if(hor <= 7 && hor >=0 && ver >= 0 && ver <= 7){
    			board[ver][hor] = count;
    			traverse(count + 1, ver-1, hor+2);
    		}
    		return false;
    	}
     
     
    	public static boolean traverse(int count, int ver, int hor){
     
    	board[ver][hor] = count;		//store the count number at that location at the board
     
    	if(count >= 64){
    		return true;
    	}
     
    	//up 2 left 1
    	else if (ver > 1 && hor > 0 && board[ver-2][hor-1] == 0 && traverse(count + 1, ver-2, hor-1))    
              return true;    
        //up 2 right 1
        else if(ver > 1 && hor < 7 && board[ver-2][hor+1] == 0 && traverse(count + 1,ver-2,hor+1))    
             return true;  
     
        //down 2 right 1
        else if(ver < 6 && hor < 7 && board[ver+2][hor+1]== 0 && traverse(count + 1,ver+2,hor+1))
        	 return true;
        //down 2 left 1
        else if(ver < 6 && hor > 0 && board[ver+2][hor-1]== 0 && traverse(count + 1,ver+2,hor-1))
        	 return true;
     
        //right 2 up 1
        else if(hor < 6 && ver > 0 && board[ver-1][hor+2]== 0 && traverse(count + 1,ver-1,hor+2))
        	 return true;
        //right 2 down 1
        else if(hor < 6 && ver < 7 && board[ver+1][hor+2]== 0 && traverse(count + 1,ver+1,hor+2))
        	return true;
     
        //left 2 up 1
        else if(hor > 1 && ver > 0 && board[ver-1][hor-2]== 0 && traverse(count + 1,ver-1,hor-2))
        	 return true;
        //left 2 down 1
        else if(hor > 1 && ver < 7 && board[ver+1][hor-2]== 0 && traverse(count + 1,ver+1,hor-2))
        	 return true;
     
        if(count >= 57)
        	globalCount = count;		//test to see how high the program gets to, it does not get past a count of 57;
     
        return false;
     
    }
    	public static void init(int[][] array){
    		for(int i = 0; i < array[0].length; i++){
    			for(int a = 0; a < array.length; a++){
    				array[i][a] = 0;
    			}
    		}
    	}
    	public static void print(int[][] array){
    		for(int i = 0; i < array[0].length; i++){
    			System.out.println();
    			for(int a = 0; a < array.length; a++){
    				System.out.print(" " + array[i][a] + " ");
    			}
    		}
    	}	
    	public static boolean boardTraversed(int board[][]){
    		//checks to see if board is not traversed
    		for(int i = 0; i < board[0].length; i++)
    			for(int a = 0; a < board.length; a++)
    				if(board[i][a] == 0)
    					return false;
    		return true;
    	}
     
    }
    Last edited by budder8818; February 4th, 2009 at 02:42 PM.


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