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See: https://adventofcode.com/2023/day/1
** Part 1
*** Purpose
Given a list of lines of characters, each with a minimum of one integers:
#+begin_example
1abc2
pqr3stu8vwx
a1b2c3d4e5f
treb7uchet
#+end_example
Reduce each line to the first and last integer, then add all lines together. If a line contains a single integer, count that integer twice.
*** Method
The solution to this is obvious---filter the non-numeric characters out of the each line, index the first and last characters, and then make the summation.
** Part 2
*** Purpose
The next part now asserts that some spelt out numbers are unaccounted for. For example:
#+begin_example
two1nine
#+end_example
Should return the digit "29". We must calculate the new sum, with this rule in place.
*** Method
With this addition, it makes the most sense to perform some cleaning on each input string---substitute spelt numbers for actual numbers, then send it down the usual processing.
Lots of code was required to make this work---also noteworthy, is that this useful piece of information is not in the instructions:
#+begin_example
twone -> 21
#+end_example
because a letter is shared.
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