Sudoku Solver in c

/********************************** **************************
*** Dipl.- Inf. Detlef Hafer
*** D-91058 Erlangen (Germany)
********************************** ***************************/

#include "stdio.h>"
#include "stdlib.h"
#include "string.h"

#define BACK -1
#define FORWARD 1
#define NSIZE 9
#define BOOL bool
#define FALSE false
#define TRUE true

int F[NSIZE][NSIZE];

#if _DEBUG
static int M[NSIZE][NSIZE] = { {1, 6, 4, 0, 0, 0, 0, 0, 2},
{2, 0, 0, 4, 0, 3, 9, 1, 0},
{0, 0, 5, 0, 8, 0, 4, 0, 7},

{0, 9, 0, 0, 0, 6, 5, 0, 0},
{5, 0, 0, 1, 0, 2, 0, 0, 8},
{0, 0, 8, 9, 0, 0, 0, 3, 0},

{8, 0, 9, 0, 4, 0, 2, 0, 0},
{0, 7, 3, 5, 0, 9, 0, 0, 1},
{4, 0, 0, 0, 0, 0, 6, 7, 9} };

#endif

static BOOL findnumber (int z, int s)
{
int u = (z/3)*3;
int v = (s/3)*3;
int m = F[z][s];
F[z][s] = 0;

for (int t = m+1; t <= NSIZE; t++)
{
for (int i = 0; i < NSIZE; i++)
{
div_t q = div(i,3);
if ((F[i][s] == t) || (F[z][i] == t) || F[u+q.quot][v+q.rem] == t)
break;
}
if (i == NSIZE )
{
F[z][s] = t;
return TRUE;
}
}
return FALSE;
}

BOOL soduko (void)
{
BOOL bFix[NSIZE][NSIZE];
int r = FORWARD;

#if _DEBUG
memcpy(F, M, sizeof(M));
#endif

for (int i = 0; i < NSIZE; i++)
for (int j = 0; j < NSIZE; j++)
bFix[i][j] = (F[i][j] != 0);

i = 0;
while ( (i >= 0) && (i < NSIZE*NSIZE) )
{
div_t q = div(i,NSIZE);
int z = q.quot;
int s = q.rem;

if ( ! bFix[z][s])
{
if ( ! findnumber(z,s))
r = BACK;
else
r = FORWARD;
}
i += r;
}
if ( i < 0)
{
// no solution
return FALSE;
}
return TRUE;
}

int main()
{
soduko();


for (int i = 0; i < NSIZE; i++)
{
for (int j = 0; j < NSIZE; j++)
{
printf("%d ",M[i][j]);
}
printf("\n");
}
printf("\n");
printf("\n");

for (int i = 0; i < NSIZE; i++)
{
for (int j = 0; j < NSIZE; j++)
{
printf("%d ",F[i][j]);
}
printf("\n");
}


}

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