project euler 26:Reciprocal cycles

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.

 

##运用了python的decimal模块取小数点精度,然后转换成str格式查找是否有重复的,从而计算出重复的长度。

#控制在1S内~



import
decimal decimal.getcontext().prec = 100 import time start = time.time() d = 7 l = 6 for i in range(1,1000): s = str(decimal.Decimal(1)/decimal.Decimal(i)) for j in range(len(s)): temp = s[j+3:].find(s[j:j+3]) if temp > 0 and 3+temp > l: d = i l = 3 + temp # print(d,l) decimal.getcontext().prec = 100 + l break print(d,l) print(time.time()-start)
>>> 
983 982
0.6900279521942139
>>> 

 

posted on 2016-05-05 16:18  zhourong1104  阅读(236)  评论(0编辑  收藏  举报