ProjectEuler/c/0007.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>

struct primes_da {
	uint64_t *data;
	uint64_t size;
	uint64_t cap;
};


bool isprime(uint64_t n);
void primes_fill(struct primes_da *primes);

int
main(int argc, const char **argv)
{
	uint64_t res = 0;
	uint64_t target = 10001;
	struct primes_da primes = {0};

	primes.cap = target + 1;
	primes.data = calloc(primes.cap, sizeof(uint64_t));
	primes.size = 0;

	primes_fill(&primes);
	res = primes.data[target-1];

	printf("Result = %ld!\n", res);

	free(primes.data);
	(void) argc; (void) argv;
	return 0;
}

bool
isprime(uint64_t n)
{
	uint64_t i = 0;
	if ( (n & 1) == 0 ) {
		return ( n == 2 );
	}

	for ( i = 2; i < n; ++i ) {
		if ( (n % i) == 0 ) {
			return false;
		}
	}
	return true;
}

void
primes_fill(struct primes_da *primes)
{
	uint64_t i = primes->size;
	if ( i == 0 ) {
		i = 2;
	}
	for ( ; primes->size < primes->cap; ++i ) {
		if ( isprime(i) ) {
			primes->data[primes->size++] = i;
		}
	}
}