Here are the credits:

• tobyink for the basic algorithm and the boldness to step away from regexes.
• sundialsvc4 for the final check whether or not the solution is found,
• Eily to spot it in and extract it from sundialsvc4's writeup,
• BrowserUK pointing out that the first version didn't work,
• and to the Monastery for not expelling people loving to post code instead of lectures.

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