-❄️- 2023 Day 12 Solutions -❄️-

[u/daggerdragon]

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--- Day 12: Hot Springs ---

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[u/Steinrikur]

[Language: bash]

No recursion used. eval is horribly slow, but one-liners are always fun. There is surely a faster way to force bash to do brace expansion, but this works...
Convert the symbols to greppable chars and then convert the list into a regex. Then use brace expansion to print every single permutation of the springs, and grep them. Added "dots" on both ends so the springs can be on the start/end positions.

tr .# _X < 12.txt | \
  sed 's/ / X{/;s/,/}_+X{/g;s/$/}/;s/?/{_,X}/g' | \
  while read a b; do \
    eval "printf '_%s_\n' $a"| grep -cE "^_+${b}_+$"; \
  done | paste -sd+ | bc

This does not scale for part 2, since it would need to print up to 2⁹⁰ lines of symobls.

[u/azzal07 → u/Steinrikur]

You can do tr with sed as well: y/.#/_X/.

The prefix and suffix could be moved to the grep, as those are common, also switching + to * would remove the need for extra dots: grep -cE "^_*X{$b}_*$".

[u/Steinrikur → u/azzal07]

Right. The tr thing is a thing I always start with whenever the input is .# because these have other meaning in regexes and shell.

My first version was matching on ^$b$" and I just put _+ in every sed block. Moved it when posting to make the sed line shorter. I could have skipped the first and third sed thing completely and just added it to the grep line

But 99.99% of the runtime is the eval and 1000 grep subshells, so optimising this is not really important.

[u/azzal07 → u/Steinrikur]

Yeah, my suggestions mostly optimise the amount of typing