A N- Queen Problem Solution.......

Description : This is NQueens' problem. Here n queens will have to be placed in (n x n) matrix in such a way that none will meet any other wile moving horizontally, vertically or along diagonal with respect to its position. The program is able to take any input, but for better output try it with not more than 23.


/*@@ Problem : This is n-Queen problem.

@@ Description : To place n queens in (n x n) matrix such that no queen meets another while moving    along the row, col or diagonal with respect to to its position.

@@ Done by : Biswajit Debnath.

@@ University : RajaBazar Science College(Calcutta University), Kolkata

@@ E-mail : biswajitdebnathrbsc@yahoo.co.in

*/
THIS PROGRAM IS WRITTEN BY Mr. BISWAJEET DEBANTH....


#include "iostream.h"

#include "ctype.h"

#include "stdlib.h"

#include "stdio.h"

#include "conio.h"

void check(int, int, char [100][100]);
void print(char [100][100]);
int no_of_queens, queen = 2, flagrow = 0, flagcol = 0;
int count = 1;
char ch, response_row, response_col;
int main(void)
{
int row, col, i;
char board[100][100], response;
clrscr();
printf(" This is n-queen problem.Enter the number of
queens(say n)
and watch how computer places them
in (n x n) matrix
such that none can
meet another moving along horizontally,
vertically
or digonally.");

printf("Enter the number of queens : ");
scanf("%d", &no_of_queens);
if(no_of_queens > 23)
{
printf("Thought the program is OK for any queen value.But
due the configuration of the output screen the output will be
tranketed (A very large queen number may cause the system stackoverflow).
So it is highly recommended that you run the program withmaximum queen number 23...");

printf("Want to continue(Y/N)?");
fflush(stdin);
scanf("%c", &response);
if(toupper(response) == 'N')
return (0);
}
else
 if(no_of_queens < 3)
{
printf("The number of Queen must be greater than 3.");
getch();
return (0);
}
printf("Want a row number below the board(Y/N) : ");
fflush(stdin);
response_row = (char)getchar();
if(toupper(response_row) == 'Y')
flagrow = 1;
printf("Want a column number below the board(Y/N) : ");
fflush(stdin);
response_col = (char)getchar();
if(toupper(response_col) == 'Y')
flagcol = 1;
clrscr();
printf("M/c in work ! Please Wait...");
// This for-loop is used for checking all the columns of row 0 only...
_setcursortype(_NOCURSOR);
for(col = 0; col < no_of_queens; col++)
{
memset(board, '-', sizeof(board));
check( 0, col, board );
}
clrscr();
printf("Thank you for seeing this program through.");
getch();
return (0);
}
void check( int r, int c, char board[100][100] )
{
int i, j;
// Terminating condition for the recursion...
if ( ( r == no_of_queens ) && ( c == 0 ))
{
clrscr();
printf(" (%d-Queen) Set : %d
, no_of_queens, count++);
print( board );
fflush(stdin);
ch = (char)getch();
clrscr();
if(ch == 'e')
exit (0);
printf("M/c in work ! Please Wait...");
}
// Vertical check...
for(i = 0; i < r; i++)
{
if ( board[i][c] == queen)
return;
}
// Horizontal check...
for(j = 0; j < c; j++)
{
if ( board[r][j] == queen)
return;
}
// Left-Diagonal check...
i = r; j = c;
do
{
if ( board[i][j] == queen )
return;
i--; j--;
}
while( i >= 0 && j >= 0 );
// Right-Diagonal check...
i = r; j = c;
do
{
if ( board[i][j] == queen )
return;
i--; j++;
}while( i >= 0 && j < no_of_queens );

// Placing the queen if the ckecked position is OK...
board[r][c] = queen;
r++;
// This for-loop is used for checking all the columns for each row
//starting from 1 upto the end...
for(int p = 0; p < no_of_queens; p++)
check(r, p, board);
for(int h = 0; h < no_of_queens; h++)
board[r - 1][h] = '-';
}
void print(char board[100][100])
{
for(int i = 0; i < no_of_queens; i++)
{
if(flagrow == 1)
printf("%3d", i + 1);
for(int j = 0; j < no_of_queens; j++)
{
if(board[i][j] == queen)
{
textcolor(RED);
cprintf("%3c", queen);
}
else
{
textcolor(8); //dark gray
cprintf("%3c", 22);
}
}
printf("
);
}
textcolor(7);
if(flagcol == 1)
{
if(flagrow)
printf(" ");
for(i = 0; i < no_of_queens; i++)
printf("%3d", i + 1);
}
gotoxy(62, 1);
printf("Press E to exit.");
textcolor(7);
}