APL
I'm using this year's AoC to learn (Dyalog) APL, so this is most likely a pretty terrible solutions. I would've liked to use ⍣
instead of of my imitation of a while loop with a recursive function, but I couldn't figure out how to get to the number of iterations ⍣ performed to arrive at the destination. If someone here knows how to do that (or has other suggestions for improvement) I'm open for suggestions.
⎕IO ← 0 ⍝ use 0-based indexes
I←⌷⍨∘⊃⍨⍤0 99 ⍝ "sane" indexing
⎕PP←17 ⍝ print integers with up to 17 significant digits without use of scientific notation
input←⊃⎕NGET'inputs/day8.txt'1
instructions←⊃input
p←↑{0 2 4 I{6⍴⎕CSV⍠'Widths'(3 4 3 2 3 1)⊢⍵'S'1}⍵}¨ 2↓input
nodes←,1↑[1]p
L←(⍳⍴nodes) ∘.{nodes[⍺]≡⍵ 1 ⌷p} ⍳⍴nodes
R←(⍳⍴nodes) ∘.{nodes[⍺]≡⍵ 2 ⌷p} ⍳⍴nodes
S←(⊃(+.×)/{'R'≡⍵:R ⋄ ⍵≡'L':L}¨⌽instructions)
⎕←(≢instructions) × {⍺←0 ⋄ ⍵[⍸'ZZZ'∘≡¨nodes]: ⍺ ⋄ ⍺+1 ∇ S+.×⍵}'AAA'∘≡¨nodes ⍝ part 1
⎕←∧/(≢instructions) × {⍺←0 ⋄ 0≡+/⍵[⍸~('Z'∘=⊢/)¨nodes]: ⍺ ⋄ ⍺+1 ∇ S+.×⍵}¨{(⍳≢nodes)=⍵}¨⍸('A'∘=⊢/)¨nodes ⍝ part 2
APL
I finally managed to make use of ⍣ :D