#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/sem.h>

#define P(s,i) { \
   struct sembuf pop; \
   pop.sem_num = i; \
   pop.sem_op = -1; \
   pop.sem_flg = 0; \
   semop(s, &pop, 1); \
}

#define V(s,i) { \
   struct sembuf vop; \
   vop.sem_num = i; \
   vop.sem_op = 1; \
   vop.sem_flg = 0; \
   semop(s, &vop, 1); \
}

int greedychoice ( int *M )
{
   int t;

   for (t=5; t>=1; --t) {
      if ((t <= M[0]) && (t != M[1]) && (t != M[2]) && (t != M[3]))
         return t;
   }
   return 0;
}

void playgame ( int pno, int shmid, int semid )
{
   int *M, mysum, npno, t, i;

   M = shmat(shmid,0,0);
   npno = pno + 1; if (npno == 3) npno = 0;
   mysum = 0;
   P(semid,pno);
   if ((pno == 2) && (M[4] == 0)) { printf("\t"); fflush(stdout); }
   while (M[0]) {
      t = greedychoice(M);
      M[0] -= t;
      M[1] = M[2];
      M[2] = M[3];
      M[3] = t;
      ++M[4];
      mysum += t;
      printf("%s%d%s", (pno) ? "\t" : "", t, (pno == 2) ? "\n" : ""); fflush(stdout);
      if (M[0] == 0) printf("%s------------------\n", (pno == 2) ? "" : "\n");
      V(semid,npno);
      P(semid,pno);
   }
   V(semid,npno);
   for (i=0; i<pno; ++i) printf("\t");
   printf("Player %d: Total = %d\n", pno, mysum);
   shmdt(M);
   exit(0);
}

int main ( int argc, char *argv[] )
{
   int N, pno, *M;
   int shmid, semid;

   srand((unsigned int)time(NULL));
   N = (argc > 1) ? atoi(argv[1]) : 100;

   shmid = shmget(IPC_PRIVATE, 5 * sizeof(int), 0644 | IPC_CREAT);
   M = (int *)shmat(shmid, 0, 0);
   M[0] = N; M[1] = M[2] = M[3] = 0; M[4] = 0;

   semid = semget(IPC_PRIVATE, 3, 0644 | IPC_CREAT);
   semctl(semid, 0, SETVAL, 0);
   semctl(semid, 1, SETVAL, 0);
   semctl(semid, 2, SETVAL, 0);

   for (pno=0; pno<3; ++pno) {
      if (!fork()) playgame(pno,shmid,semid);
   }

   printf("------------------\nP0\tP1\tP2\n------------------\n");

   pno = rand() % 3;
   V(semid, pno);

   for (pno=0; pno<3; ++pno) wait(NULL);

   shmdt(M); shmctl(shmid, IPC_RMID, 0);
   semctl(semid, IPC_RMID, 0);

   exit(0);
}