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/* { dg-do run } */

/* { dg-options "-O2 -fopenmp" } */

/* { dg-require-effective-target tls_runtime } */

#include <omp.h>

#include <stdio.h>

#include <string.h>

int cnt;

#pragma omp threadprivate (cnt)

void

nqueens (char *a, int n, int pos)

{

  /* b[i] = j means the queen in i-th row is in column j.  */

  char b[pos + 1];

  int i, j;

  memcpy (b, a, pos);

  for (i = 0; i < n; i++)

    {

      for (j = 0; j < pos; j++)

        if (b[j] == i || b[j] == i + pos - j || i == b[j] + pos - j)

          break;

      if (j < pos)

        continue;

      if (pos == n - 1)

        /* Found a solution.  Could output it here.  */

        ++cnt;

      else

        {

          b[pos] = i;

          #pragma omp task

            nqueens (b, n, pos + 1);

        }

    }

}

int

main (int argc, char **argv)

{

  int n = 8;

  if (argc >= 2)

    n = strtoul (argv[1], NULL, 0);

  if (n < 1 || n > 127)

    {

      fprintf (stderr, "invalid count %d\n", n);

      return 1;

    }

  cnt = 0;

  double stime = omp_get_wtime ();

  nqueens ("", n, 0);

  printf ("serial   N %d solutions # %d time %f\n", n, cnt, omp_get_wtime () - stime);

  #pragma omp parallel

    cnt = 0;

  stime = omp_get_wtime ();

  int tempcnt = 0;

  #pragma omp parallel reduction (+:tempcnt)

    {

      #pragma omp single

        nqueens ("", n, 0);

      tempcnt = cnt;

    }

  cnt = tempcnt;

  printf ("parallel N %d solutions # %d time %f\n", n, cnt, omp_get_wtime () - stime);

  return 0;

}