/* par.ex8.36.c SJ */

/* 31) Write a "game" where all processes generate a random number 0..9,
	   compare the numbers, and the one(s) with largest number is (are) the
	   winner(s). After someone has 5 wins, all quit. Here, if there are
	   several processes with the same number, all get the winning point.
       Hint: MPI_Allreduce, MPI_MAX.

36) Modify the game of exercise 31 solving draws by new numbers. Only
    those processes that had the largest number will generate a new
    numbers, and if there was a sole winner, it wins. If even the new
    numbers generated a draw, the procedure is repeated among remaining
    processing until the winner if found.
*/


#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <mpi.h>

/* maximum number */
#ifndef NMAX
#define NMAX 4
#endif

/* number of rounds */
#ifndef WINS
#define WINS 3
#endif

/* how much to print */
#ifndef PRINT
#define PRINT 2
#endif

static int P, PID; /* used in prints in fucntins */
int playround(MPI_Comm comm);

int main(int argc, char **argv)
{
  int wins = 0, maxwins, round = 0;

  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &PID);
  MPI_Comm_size(MPI_COMM_WORLD, &P);

  srand(getpid());

  do {
	  round++;

	  wins += playround(MPI_COMM_WORLD);

	  /* find maximum of wins */
	  MPI_Allreduce(&wins, &maxwins, 1, MPI_INT, MPI_MAX, MPI_COMM_WORLD);
	  
	  if (PRINT && !PID) {
		  printf("After round %d: maximum: %d wins\n", round, maxwins);
	  }

	  fflush(stdout);
	  MPI_Barrier(MPI_COMM_WORLD);

  } while (maxwins < WINS);

  MPI_Finalize();

  exit(0);

}

int playround(MPI_Comm comm)
{
  int num, max, mebest, numbests;
  MPI_Comm newcomm;

  /* get a number */
  num = rand()%NMAX;

  if (PRINT > 1)
	  printf("%d gets %d\n", PID, num);

  /* find maximum */
  MPI_Allreduce(&num, &max, 1, MPI_INT, MPI_MAX, comm);

  /* check for draws */

  /* did I possibly win */
  if (num == max)
	  mebest = 1;
  else
	  mebest = 0;

  MPI_Allreduce(&mebest, &numbests, 1, MPI_INT, MPI_SUM, comm);

  if (numbests == 1) {
	  if (PRINT && mebest)
		  printf("%d wins by %d\n", PID, num);
	  return mebest;
  } else {
	  /* regame, just best participate in new group */
	  MPI_Comm_split(comm, mebest, 0, &newcomm);
	  if (mebest) {
		  if (PRINT)
			  printf("%d has draw %d (%d same)\n", PID, num, numbests);
		  mebest = playround(newcomm);
	  }
	  MPI_Comm_free(&newcomm);
  }

  return mebest;
} /* playround() */