I finally got to checking the C version, and other than a pile of warnings, it's seems to be fine. I run my solution against the full test suite several times and it seems to consistently pass. I struggled a bit with edge cases though, which are somewhat underspecified, especially leading zeros in input.

Please check for leading/trailing spaces and missing null terminator in your solutoin, and I will check the tests.

I suspect the C tests are broken--I get two failures like this on an attempt:

https://puu.sh/G5veN/a195539ae1.png