/* The 3SUM problem: given a multiset S of n integers, are there
 * elements a, b, c in S such that a + b + c = 0?
 */

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

static bool search(long const *S, long n)
{
    long i, j, k;

    for (i = 0; i < n; i++)
        for (j = 0; j < n; j++)
            for (k = 0; k < n; k++)
                if ((S[i] + S[j] + S[k]) == 0)
                    return true;

    return false;
}

static void randomize(long *S, long n, float theta)
{
    long i;

    for (i = 0; i < n; i++) {
        S[i] = (random() < (theta * RAND_MAX)) ? +1 : -1;
    }
}

int main(int argc, char *argv[])
{
    /* Default parameters.  */
    long n = 1000;
    float theta = 0.5;

    /* Override default random seed.  */
    if (argc > 1)
        srandom(atol(argv[1]));

    /* Override default size n of multiset S.  */
    if (argc > 2)
        n = atol(argv[2]);

    /* Override default bias of input distribution.  */
    if (argc > 3)
        theta = atof(argv[3]);

    /* Allocate the multiset.  */
    long S[n];

    /* Initialize the multiset.  */
    randomize(S, n, theta);

    /* Kick off the search.  */
    return search(S, n);
}