Problem 918. Find the repeating decimal pattern!

Created by Matt Fig

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Write a function that takes one double input value and returns only the repeating decimal, if any, as a string. Only decimals for which all digits are part of the repeating pattern will be counted. (See the 3rd example below.) Inputs will be in the range [0 1].

If no repeating decimal is found, the function should return an empty string. Of course the repeating decimal may break down in the last bit due to floating point arithmetic, but we will ignore that.

Examples:

T = repeatingdec(7/11)  % Returns T = '63'
T = repeatingdec(1/3)   % Returns T = '3'
T = repeatingdec(5/6)    % Returns T = ''
T = repeatingdec(0)      % Returns T = '0'

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Last Solution submitted on Aug 30, 2024

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2 Comments

Andrew Newell on 20 Jun 2013

The tests are inconsistent with the statement of the problem. Finite strings like ..123451234512345 only repeat to the end of the string, then switch to zeros.

Rafael S.T. Vieira on 4 Oct 2020

The problem should specify the precision required, there are numbers that cannot be represented with doubles and are loosing significant digits. And this really becomes an issue when your test suite use less significant digits to identify repeating patterns such as in cases 7 and 10. I was able to overcome this issue by using 14 digits, but some people used 16 (If someone else is having problems that's the way to go). Moreover, Andrew is right, a number like 0.333333 is technically not a repeating decimal.

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Problem 918. Find the repeating decimal pattern!

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Problem 918. Find the repeating decimal pattern!

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