/* By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
 *
 * What is the 10 001st prime number?*/

#define _POSIX_C_SOURCE 199309L

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "projecteuler.h"

int main(int argc, char **argv)
{
    int count = 1, n = 1, target = 10001;
    double elapsed;
    struct timespec start, end;

    clock_gettime(CLOCK_MONOTONIC, &start);

    /* Brute force approach: start with count=1 and check every odd number
     * (2 is the only even prime), if it's prime increment count, until the
     * target prime is reached.*/
    while(count != target)
    {
        n += 2;
        /* Use the function in projecteuler.c to check if a number is prime.*/
        if(is_prime(n))
        {
            count++;
        }
    }

    clock_gettime(CLOCK_MONOTONIC, &end);

    elapsed = (end.tv_sec - start.tv_sec) + (double)(end.tv_nsec - start.tv_nsec) / 1000000000;

    printf("Project Euler, Problem 7\n");
    printf("Answer: %d\n", n);

    printf("Elapsed time: %.9lf seconds\n", elapsed);

    return 0;
}