Day 17 solution.

p17.dyalog

@@ -0,0 +1,14 @@
+⎕IO←0
+c←⊃¨p←⊃⎕NGET'p17.txt'1
+p←⍎¨¨'\d+'⎕S'&'¨p
+a b←(⌊/,⌈/)∊1↓¨p/⍨c='x'
+g←(1+b)1000⍴''
+to←{⍺+⍳⍵-⍺}
+{g[⍵[1] to 1+⍵[2];⍵[0]]←'#'}¨p/⍨c='x'
+{g[⍵[0];⍵[1] to 1+⍵[2]]←'#'}¨p/⍨c='y'
+d←{x y←⍵ ⋄ t←y↓g[;x] ⋄ n←1⍳⍨t∊'#~' ⋄ g[y+⍳n;x]←'|' ⋄ _←f⍣(n<t⍳'|')⊢x(y+n-1)}
+e←{x y←⍵ ⋄ t←⍺∊⍨x⌽y⌷g ⋄ x+(-1⍳⍨⌽t)(t⍳1)}
+f←{x y←⍵ ⋄ i j←'| 'e ⍵+0 1 ⋄ k l←'#'e ⍵ ⋄ g[y;(i⌈k)to j⌊l]←'|~'⊃⍨⍱/t←i l>k j ⋄ ⍱/t:∇⍵-0 1 ⋄ d¨y,⍨¨t/(i-1)j}
+d 500 0
++/,'|~'∊⍨a↓g ⍝ part 1
++/,'~'=a↓g ⍝ part 2