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xpqz/day9.apl

Last active December 10, 2021 17:02
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day9.apl
⍝ Blatantly plagiated from @rak1507
data←↑⍎¨¨⊃⎕NGET'../d/9'1
shifts←{(⍺,2⊣/⍵)(2⊢/⍵,⍺)(2⊢⌿⍵⍪⍺)(⍺⍪2⊣⌿⍵)}
lowpoints←data<⊃⌊/10 shifts data
+/1+data[⍸lowpoints] ⍝ part 1
fill←{(×⍵)×⍵⌈⊃⌈/0 shifts ⍵}⍣≡{(2+⍳+/,⍵)@⊢⍵}9≠data
×/3↑{⍵[⍒⍵]}⊢∘≢⌸(∊fill)~0 ⍝ part 2
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