Advent of Code day 10

10.dyalog

in←↑⊃⎕nget '10.input' 1 ⋄ p←'#'=in

can_see←{⍺≡⍵:0
          0=+/¯1↓{p[⍵[0];⍵[1]]}¨⍺ els_btwn ⍵ }

els_btwn←{ ⍺≡⍵:⍬
           n←⍺+(⍺ slope_btwn ⍵)
           (⊂n),(n ∇ ⍵) }     

slope_btwn←{{⍵÷(∨/⍵)}-⍺-⍵}                                                         
visible_pts←{ cur←↑⍵
              +/{(cur can_see ↑⍵) ∧ ⍵⌷p}¨,{⍵∘.,⍵}⍳21}
  
⎕←pt1←⌈/,(21 21 ⍴(visible_pts¨,{⍵∘.,⍵}⍳21))∧p

⎕div←1 
target←11 11 ⋄ shape←21 21
els←((⍳shape[0])∘.,(⍳shape[1]))
angles←shape ⍴{(180÷(○1))ׯ3○(÷/target slope_btwn ⍵)}¨,els

quad←{ r←(⍺-1)⌷1 1 0 0 ⋄ b←(⍺-1)⌷0 1 1 0
       rfn←(⍺-1)⌷'↓' '↓' '↑' '↑' ⋄ bfn←(⍺-1)⌷'↑' '↓' '↓' '↑'
       (target[1]+r)(⍎rfn)[1](target[0]+b)(⍎bfn)⍵ }
zapped←⍬

zap←{ line←↑(⍵-1)⌷(0,target[1]) (target[0],shape[1]-1) ((shape[0]-1),target[1]) (target[0],0)
      zapped,←{ 0<+/p[⍵]:1↑p[⍵]/⍵
                ⍬ }(target els_btwn line)
      zapped,←{({(target can_see ⍵)∧(⍵⌷p)}¨⍵)/⍵}(, ⍵ quad els)[⍋, ⍵ quad angles] }