Desafio Soma de primos

// http://www.forum-invaders.com.br/vb/showthread.php/42846-DESAFIO-Soma-de-primos

#include <stdio.h>
#include <math.h>
#include <windows.h>

#define BUFFER_SIZE 128

typedef struct {
    int count;
    int* primes;
} primes_t;

primes_t* primesCreate() {
    primes_t* a = malloc(sizeof(primes_t));
    a->count = 1;
    a->primes = malloc(sizeof(int) * BUFFER_SIZE);
    a->primes[0] = 2;
    return a;
}

int isPrime(primes_t* a, int n)
{
    int s = sqrt(n) + 1;
    int i;

    for(i = 0; i < a->count; ++i) {
        if(a->primes[i] > s)
            return 1;
        if(n % a->primes[i] == 0)
            return 0;
    }

    return 1;
}

void primesMake(primes_t* a) {
    if(a->count % BUFFER_SIZE)
        a->primes = realloc(a->primes, sizeof(int) * BUFFER_SIZE * (int)((a->count / BUFFER_SIZE) + 1));

    int i = a->primes[a->count - 1];
    while(!isPrime(a, ++i));
    a->primes[a->count++] = i;
}

void primesDestroy(primes_t* a) {
    free(a->primes);
    free(a);
}

int zaz(primes_t* a, int v, int i, int f) {
    int c = 0;
    for(; i < a->count; ++i) {
        int r = v - a->primes[i];
        if(r > 0)
            c += zaz(a, r, i, 0);
        else if(r == 0 && f == 0) {
            return ++c;
        } else
            return c;
    }

    return c;
}

int main(int argc, char **argv)
{
    unsigned int s = GetTickCount();
    int n = 1;
    int c = 0;
    primes_t* a = primesCreate();

    do {
        ++n;
        while(n > a->primes[a->count - 1] + 1)
            primesMake(a);
    } while((c = zaz(a, n, 0, 1)) < 5000);

    primesDestroy(a);

    unsigned int e = GetTickCount() - s;

    printf("result %d %d\n", c, n);
    printf("elapsed %d milliseconds", e);
    return 0;
}