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.

1.package euler;  
2.  
3.import java.util.HashSet;  
4.import java.util.Set;  
5.  
6./** 
7. *  
8. * @author hongfa.yy 
9. * @version 2013-2-6 下午4:48:51 
10. */  
11.public class Problem26 {  
12.    public static void main(String[] args) {  
13.        int max = 0;  
14.        int max_d=0;  
15.        for (int i = 1; i < 1000; i++) {  
16.            int count = count(i);  
17.            if (count > max){  
18.                max_d=i;  
19.                max = count;  
20.            }  
21.                  
22.        }  
23.        System.out.println(max_d);  
24.    }  
25.  
26.    private final static int decimalism = 10;  
27.  
28.    private static int count(int denominator) {  
29.        Set<Integer> set = new HashSet<>();  
30.        int mode = 1 * decimalism % denominator;  
31.        while (mode != 0) {  
32.            if (!set.contains(mode))  
33.                set.add(mode);  
34.            else  
35.                return set.size();  
36.            mode = mode * decimalism % denominator;  
37.        }  
38.  
39.        return 0;  
40.    }  
41.}