--- Day 10: Elves Look, Elves Say ---
Today, the Elves are playing a game called look-and-say. They take turns making sequences by reading aloud the previous sequence and using that reading as the next sequence. For example, 211
is read as "one two, two ones", which becomes 1221
(1
2
, 2
1
s).
Look-and-say sequences are generated iteratively, using the previous value as input for the next step. For each step, take the previous value, and replace each run of digits (like 111
) with the number of digits (3
) followed by the digit itself (1
).
For example:
1
becomes11
(1
copy of digit1
).11
becomes21
(2
copies of digit1
).21
becomes1211
(one2
followed by one1
).1211
becomes111221
(one1
, one2
, and two1
s).111221
becomes312211
(three1
s, two2
s, and one1
).
Starting with the digits in your puzzle input, apply this process 40 times. What is the length of the result?