26.c

/*
 * A unit fraction contains 1 in the numerator. The decimal representation of the unit fractions with denominators 2 to 10 are given:
* 
* 1/2  = 0.5
* 1/3  = 0.(3)
* 1/4  = 0.25
* 1/5  = 0.2
* 1/6  = 0.1(6)
* 1/7  = 0.(142857)
* 1/8  = 0.125
* 1/9  = 0.(1)
* 1/10 = 0.1
*
* Where 0.1(6) means 0.166666..., and has a 1-digit recurring cycle. It can be seen that 1/7 has a 6-digit recurring cycle.
* 
* Find the value of d < 1000 for which 1/d contains the longest recurring cycle in its decimal fraction part.
*/

#include <stdio.h>

int main(int argc, char const *argv[])
{
  int n, i, len, maxlen, maxn;
  maxlen = 0;
  for (n = 2; n <= 1000; n++) {
    int rest = 1;
    int r0;
    for (i = 0; i < n; i++)
      rest = (rest * 10) % n;
    r0 = rest;
    len = 0;
    do {
      rest = (rest * 10) % n;
      len++;
    } while (rest != r0);
    if (len > maxlen) {
      maxn = n;
      maxlen = len;
    }
  }
  printf("result: %d: %d\n", maxn, maxlen);
  return 0;
}