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

const int naptime = 100000; // How long the program will wait before clearing 
                            // the screen and printing a new board.

int i,j,di,dj; // The indices.
int step=0;    // The nth step. 
int seed;      // A seed for the random-number generator.
int points=0;

const int xsiz=30,ysiz=50; // The size of the board. 
const int nsteps = 335;    // Maximum number of iterations.

typedef int gridfunc[xsiz*ysiz]; // A grid is represented by a 1D array.
gridfunc b, nb;                  // The current and next boards.

const int INDEX2D(int i,int j) { // For indices i and j, returns the proper index
    return i*ysiz+j;             // of the grid element within the 1D array.
}

void randb(gridfunc &b) { // Produces a random board.
  seed = getpid();        // The seed is equal
  seed = 4570;            // to the process ID.
  srand(seed);            // The RNG is seeded.
  int r;                  // A random number.
  for (i=1; i<xsiz-1; i++)   
    for (j=1; j<ysiz-1; j++) {
       r = rand()%100+1;       // Produce a random number.
       int cc = INDEX2D(i,j);  // Find the 1D index.
       if (r < 10)  b[cc] = 1; // If the random number is less than 10,
       else         b[cc] = 0; // let this grid element be a 1; 
                               // otherwise let it be a 0.
    }
}

// Print a board.
void pboard(gridfunc &b) {
    usleep((useconds_t)naptime); // Wait for a while
    system("clear");             // then clear the screen.
    for (i=0; i<xsiz; i++) {
        for (j=0; j<ysiz; j++) {
            int cc = INDEX2D(i,j);
            if (b[cc] == 0) printf(" ."); // Span the board; if the element is 0, 
            else            printf(" O"); // print a dot, otherwise print an O.
        }
        printf("\n");
    }
    printf("\nLast step: %d, seed=%d\n", step, seed);
}

void evolve() {
    points = 0; // Set points to 0, initially.
    for (int i=1; i<xsiz-1; i++) {
        for (int j=1; j<ysiz-1; j++) { 
            int s=0;               // s is initially 0.
            int cc = INDEX2D(i,j); 
            for (int di=-1; di<=1; di++) {
                for (int dj=-1; dj<=1; dj++) {
                    int cn = INDEX2D(i+di,j+dj);
                    if (di==0 && dj==0) // If this pixel, do nothing.
                        ;
                    else if (b[cn]!=0)  // If the neighboring pixel,
                        s++;            // is alive, increment sum.
                }
            }
            if (b[cc] >  0 && s==2)      // If the element is alive and the sum is 2,
                nb[cc] = 1;              // stay alive.
            else if (b[cc] >= 0 && s==3) // If the sum is 3, 
                nb[cc] = 1;              // remain alive or be born.
            else if (b[cc] == 1 && s> 3) // If the element is alive and the sum is greater than 3,
                nb[cc] = 0;              // the element dies from overcrowding.
            else                         // Otherwise 
                nb[cc] = 0;              // the element dies or remains dead.
        }
    }
    for (int i=0;i<xsiz;i++) {
        for(int j=0;j<ysiz;j++) {
            int cc = INDEX2D(i,j); // Set each element of this board to the corresponding 
            b[cc] = nb[cc];        // element of the new board. 
            if(nb[cc])
                points++;          // A point is earned for each living cell.
        }
    }
}

int main() {
    randb(b);
    for (step=1; step<=nsteps; step++) { // Iterate for nsteps.
        pboard(b);
        evolve();
        if(points == 0) break;           // If every cell is dead, stop.
    }
    pboard(b);
    printf(" =) \n");
    return 0;
}