/*
	Birthday matching problem: 
		compute a probability through simulation
*/

#include <stdlib.h>
#include <stdio.h> /* for srand48(), drand48() */

int n = 50; /*  number of peoples */
int n_trials = 1000000;
int B[365];

int main (int argc, char *argv[] )
{

	int i,j;
	int d;
	int match = 0;
	int seed = 20110615;

	srand48(seed);

	for (j=0; j<n_trials; j++) {

		for (i=0; i<365; i++) {
			B[i]= -1;
		}

		for (i=0; i<n; i++) {
			d = (int)(drand48()*365.0);
			if ( B[d] > -1 ){
//				printf("already exists d=%d, B[d]=%d, i=%d\n", d, B[d], i);	
				match++;
				break;
			}
			else{
				B[d] = i;
			}
		}
	}
	printf("prob = %.8lf \n", (double)match/(double)n_trials);

	return 0;
}