
Jan 8th, 2002, 04:23 AM
#1
Thread Starter
Hyperactive Member
Problem with recursive solution of "Knight's Tour".
Hi,
I am working with the problem 'Knight's tour' and my program's meant to move the knight to as many squares as possible on a chess board while not revisiting any squares. Can anoyone be kind enough to make my code work or simply post a better and simpler solution. I mean, i cna't learning anything without seeing examples, and i'm really stuck. I also tried the iterative version and still could'nt get it to work. Pls help.
thnx in advance
Code:
/* Knight's Tour ( recursive version ) */
#include <stdio.h>
/* 'col' = column */
int knights_tour( int startingRow, int startingCol, int moveNumber ); /* returns the number of moves made */
int out_of_bounds( int nextRow, int nextCol ); /* check if next move is off the board */
int visited( int nextRow, int nextCol, int board[][ 8 ] ); /* check if next square is visited already */
int main()
{
printf( "***Knight's Tour***" );
knights_tour( 0, 0, 0 );
return 0;
)
int out_of_bounds( int nextRow, int nextCol )
{
/* Returns 1 if out of bounds.
Returns 0 if O.K. */
if ( nextRow < 0  nextRow > 7 )
return 1;
if ( nextCol < 0  nextCol > 7 )
return 1;
/* O.K. */
return 0;
}
int visited( int nextRow, int nextCol, int board[][ 8 ] )
{
/* Returns 1 if visited.
Returns 0 if not visited. */
if ( board[ nextRow ][ nextCol ] == 1 )
return 1;
return 0;
}
int knights_tour( int startingRow, int startingCol, int moveNumber )
{
int board[ 8 ][ 8 ] = { 0 };
/* moveNumbers: 0 1 2 3 4 5 6 7 */
int horizontal[ 8 ] = { 2, 1, 1, 2, 2, 1, 1, 2 };
int vertical[ 8 ] = { 1, 2, 2, 1, 1, 2, 2, 1 };
int temp1, temp2;
int currentRow, currentCol;
int totalMoves = 0;
if ( moveNumber > 7 )
return 0;
temp1 = currentRow + vertical[ moveNumber ];
temp2 = currentCol + horizontal[ moveNumber ];
if ( out_of_bounds( temp1, temp2 ) != 1  visited( temp1, temp2, board ) != 1 ) {
board[ currentRow ][ currentCol ] = 1;
currentRow += vertical[ moveNumber ];
currentCol += horizontal[ moveNumber ];
++totalMoves;
return knights_tour( currentRow, currentCol, moveNumber + 1 ) + totalMoves;
}
}

Jan 8th, 2002, 05:14 AM
#2
transcendental analytic
1. the board is local
2. moveNumber never gets incremented
Use
writing software in C++ is like driving rivets into steel beam with a toothpick.
writing haskell makes your life easier:
reverse (p (6*9)) where p xx==0=""True=chr (48+z): p y where (y,z)=divMod x 13
To throw away OOP for low level languages is myopia, to keep OOP is hyperopia. To throw away OOP for a high level language is insight.

Jan 8th, 2002, 05:24 AM
#3
Thread Starter
Hyperactive Member
for the 'board', can i fix the problem by adding a 'board' argument in the knights_tour function? but what do u mean moveNumber is never incremented, why?
i am very new to c can you pls post a sample knights_tour function if possible?
how about this code?
Code:
/* Knight's Tour ( recursive version ) */
#include <stdio.h>
/* 'col' = column */
int knights_tour( int startingRow, int startingCol, int moveNumber, int board[][ 8 ] ); /* returns the number of moves made */
int out_of_bounds( int nextRow, int nextCol ); /* check if next move is off the board */
int visited( int nextRow, int nextCol, int board[][ 8 ] ); /* check if next square is visited already */
int main()
{
int board[ 8 ][ 8 ] = { 0 };
printf( "***Knight's Tour***" );
printf( "Number of moves made: %d \n\n", knights_tour( 0, 0, 0 , board));
return 0;
)
int out_of_bounds( int nextRow, int nextCol )
{
/* Returns 1 if out of bounds.
Returns 0 if O.K. */
if ( nextRow < 0  nextRow > 7 )
return 1;
if ( nextCol < 0  nextCol > 7 )
return 1;
/* O.K. */
return 0;
}
int visited( int nextRow, int nextCol, int board[][ 8 ] )
{
/* Returns 1 if visited.
Returns 0 if not visited. */
if ( board[ nextRow ][ nextCol ] == 1 )
return 1;
return 0;
}
int knights_tour( int startingRow, int startingCol, int moveNumber, int board[][ 8 ] )
{
/* moveNumbers: 0 1 2 3 4 5 6 7 */
int horizontal[ 8 ] = { 2, 1, 1, 2, 2, 1, 1, 2 };
int vertical[ 8 ] = { 1, 2, 2, 1, 1, 2, 2, 1 };
int temp1, temp2;
int currentRow, currentCol;
int totalMoves = 0;
if ( moveNumber > 7 )
return 0;
temp1 = currentRow + vertical[ moveNumber ];
temp2 = currentCol + horizontal[ moveNumber ];
if ( out_of_bounds( temp1, temp2 ) != 1  visited( temp1, temp2, board ) != 1 ) {
board[ currentRow ][ currentCol ] = 1;
currentRow += vertical[ moveNumber ];
currentCol += horizontal[ moveNumber ];
++totalMoves;
return knights_tour( currentRow, currentCol, moveNumber + 1 , board) + totalMoves;
}
}
Last edited by iflash; Jan 8th, 2002 at 05:32 AM.

Jan 8th, 2002, 07:24 AM
#4
Black Cat
Is this homework out of the Dietel & Dietel book? I've "helped" someone with this before and have several of the solutions, but I did it OO/C++ with a Knight class, and they didn't do OO in their class yet...
Josh
Get these: Mozilla Opera OpenBSD
I have books for sale: "MCSD in a Nutshell" and "VB Distributed Exam Cram"  PM me for details. Will also trade for a decent ATX Pentium 2 MB/CPU/RAM combo.

Jan 8th, 2002, 10:59 AM
#5
transcendental analytic
You can pass around board if you want, you can go functional all the way if you want but C++ is meant for object orientation. Don't you see what moveNumber not being incrementing means? I suppose you had an idea to start with otherways you wouldn't have come this far, maybe you've left this project for a good while like a half year or so?
Use
writing software in C++ is like driving rivets into steel beam with a toothpick.
writing haskell makes your life easier:
reverse (p (6*9)) where p xx==0=""True=chr (48+z): p y where (y,z)=divMod x 13
To throw away OOP for low level languages is myopia, to keep OOP is hyperopia. To throw away OOP for a high level language is insight.

Jan 8th, 2002, 09:58 PM
#6
Thread Starter
Hyperactive Member
Yes this problem is from the deitel book of C: How to Program.
IF possible i really need help with a recursive solution, i've already worked out the iterative solution yesterday.
thnx

Jan 9th, 2002, 08:40 AM
#7
Black Cat
Which is the recursive part? Its been a while, and I don't have the book anymore.
Josh
Get these: Mozilla Opera OpenBSD
I have books for sale: "MCSD in a Nutshell" and "VB Distributed Exam Cram"  PM me for details. Will also trade for a decent ATX Pentium 2 MB/CPU/RAM combo.

Jan 9th, 2002, 09:07 AM
#8
transcendental analytic
last line, recursion means: call itself
Use
writing software in C++ is like driving rivets into steel beam with a toothpick.
writing haskell makes your life easier:
reverse (p (6*9)) where p xx==0=""True=chr (48+z): p y where (y,z)=divMod x 13
To throw away OOP for low level languages is myopia, to keep OOP is hyperopia. To throw away OOP for a high level language is insight.
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