Computers are fast

gistfile1.c

#include "stdafx.h"
#include "time.h"

#define d 5

int _tmain(int argc, _TCHAR* argv[])
{
	time_t t = time(0);
	int a[d*d], results[d*d+1];
	for( int i=0; i<d*d; ++i ) a[i] = 0;
	for( int i=0; i<d*d+1; ++i ) results[i] = 0;

	for( int n=0; n<(1<<d*d); ++n )
	{
		// make a new a
		for( int i=0; i<d*d; ++i )
			a[i] = (n & (1<<i)) ? 1 : 0;

		// count greens
		int greens = 0;
		for( int y=0; y<d; ++y )
		{
			for( int x=0; x<d; ++x )
			{
			  int neighbors = 0;
			  if( x>0   && a[(x-1)+y*d]==1 ) neighbors++;
			  if( x<d-1 && a[(x+1)+y*d]==1 ) neighbors++;
			  if( y>0   && a[x+(y-1)*d]==1 ) neighbors++;
			  if( y<d-1 && a[x+(y+1)*d]==1 ) neighbors++;
			  if( neighbors%2==0 ) greens++;
			}
		}
		results[greens]++;
	}

	// print results
	for( int i=0; i<=d*d; ++i )
		printf( "%d: %d\n", i, results[i] );

	printf( "%d", time(0)-t );
  
	return 0;
}