Project Euler, Problem 26.

pro26.c

#include <stdio.h>
#include <malloc.h>
#include <string.h>

int num_of_cycle(int n)
{
    int ret; /* return value */
    int *rem_seen = (int *)malloc(n * sizeof(*rem_seen));
    memset(rem_seen, 0, n*sizeof(*rem_seen));

    int rem = 1;
    int length = 1;

    while (rem != 0) {
        rem = (rem * 10) % n;
        if (rem_seen[rem] > 0) {
            ret = length - rem_seen[rem];
            break;
        } else {
            rem_seen[rem] = length;
            length ++;
        }
    }


    free(rem_seen);
    return ret;
}

int main(int argc, const char *argv[])
{
    
    int i;
    int max = 0;
    int max_indx = 0;

    for (i = 2; i < 1000; i++) {
        int cycles = num_of_cycle(i);
        if (cycles > max) {
            max = cycles;
            max_indx = i;
        }
    }
    
    printf("%d\n", max_indx);

    return 0;
}