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- Run Length Decoding 49 answers
The background comes from this related challenge. Thanks, @HeyLlama!
The "Look and say" or "Say what you see" sequence is a series of numbers where each describes the last.
1 11 (one one) 21 (two ones) 1211 (one two, one one) 111221 (one one, one two, two ones) 312211 (three ones, two twos, one one) and on and on...
Given a positive integer with an even number of digits, give the previous number described by the "Look and say" pattern.
You may take input and/or give output as a list of digits rather than numbers.
The given number may not necessarily be part of sequence A005150; this is provided as an example rather than a domain specification.
11 (one 1) -> 1 21 (two 1s) -> 11 131112 (one 3, one 1, one 2) -> 312 234186 (two 3s, four 1s, eight 6s) -> 33111166666666
This is code-golf, so the shortest answer in each language wins!