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nqueens.c
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nqueens.c
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#include <stdio.h>
#include "libft.h"
static void print_board(int *sol, int n)
{
int i;
int j;
static int solutions;
solutions++;
printf("solution %i\n", solutions);
i = -1;
while (++i < n)
{
j = -1;
while (++j < n)
{
if (sol[i] == j)
printf("Q ");
else
printf(". ");
}
printf("\n");
}
printf("\n");
}
void nqueens(int *sol, char *fr, char *fpd, char *fsd, int i, int n)
{
int k;
if (i == n)
print_board(sol, n);
else
{
k = -1;
while (++k < n)
{
if (fr[k] && fpd[i - k + n - 1] && fsd[i + k])
{
/* put the queen */
sol[i] = k;
/* update dp arrays */
fr[k] = 0;
fpd[i - k + n - 1] = 0;
fsd[i + k] = 0;
/* call recursion for next column */
nqueens(sol, fr, fpd, fsd, i + 1, n);
/* remove queen and update dp arrays */
sol[i] = -1;
fr[k] = '1';
fpd[i - k + n - 1] = '1';
fsd[i + k] = '1';
}
}
}
}
int main(int argc, char **argv)
{
/* sol is an integer array of columns, with each cell
* containng row index where the queen is placed */
int *sol;
/* dp arrays for fast checking valid positions */
char *free_rows;
char *free_pdiags;
char *free_sdiags;
int i;
int n;
if (argc != 2)
return (0);
n = atoi(argv[1]);
sol = malloc((n + 1) * sizeof(*sol));
free_rows = malloc(n * sizeof(*free_rows));
/* the amount of diags is 2n-1, and +1 is for terminating '\0'" */
free_pdiags = malloc(((2 * n - 1) + 1) * sizeof(*free_pdiags));
free_sdiags = malloc(((2 * n - 1) + 1) * sizeof(*free_sdiags));
i = -1;
while (++i < n)
sol[i] = -1;
free_rows[n] = '\0';
free_pdiags[2 * n - 1] = '\0';
free_sdiags[2 * n - 1] = '\0';
ft_bchar(free_rows, '1', n);
ft_bchar(free_pdiags, '1', 2 * n - 1);
ft_bchar(free_sdiags, '1', 2 * n - 1);
nqueens(sol, free_rows, free_pdiags, free_sdiags, 0, n);
free(sol);
free(free_rows);
free(free_pdiags);
free(free_sdiags);
}