Problem26

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.

package euler;

import java.util.HashSet;
import java.util.Set;

/**
 * 
 * @author hongfa.yy
 * @version 2013-2-6 下午4:48:51
 */
public class Problem26 {
	public static void main(String[] args) {
		int max = 0;
		int max_d=0;
		for (int i = 1; i < 1000; i++) {
			int count = count(i);
			if (count > max){
				max_d=i;
				max = count;
			}

		}
		System.out.println(max_d);
	}

	private final static int decimalism = 10;

	private static int count(int denominator) {
		Set<Integer> set = new HashSet<>();
		int mode = 1 * decimalism % denominator;
		while (mode != 0) {
			if (!set.contains(mode))
				set.add(mode);
			else
				return set.size();
			mode = mode * decimalism % denominator;
		}

		return 0;
	}
}