欧拉习题26

题目如下：

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.

还是采用暴力手段

d = 1;
for i = primes(1000)
    c = length(regexp(char(vpa(1/i,10000)),'(\d{4,}?)(\1)','match','once'))/2;
    if c > d
        d = c;  
        i
    end
end