37 lines
1.3 KiB
Standard ML
37 lines
1.3 KiB
Standard ML
datatype instruction = NOOP | DO | DONT | MUL of (int * int)
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fun numberAt (i : int) = fn (s : string) =>
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if i >= String.size s then NONE
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else SOME (Substring.takel Char.isDigit (Substring.extract (s, i, NONE)))
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fun startsWith (needle : string, haystack : string, pos : int) =
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size haystack > pos + size needle andalso String.substring (haystack, pos, size needle) = needle
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fun substrToInt (n : substring) = valOf (Int.fromString (Substring.string n))
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val file = TextIO.openIn "day_3.txt"
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val input = TextIO.inputAll file;
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TextIO.closeIn file;
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val instructions = List.tabulate ((size input), (fn i =>
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if startsWith ("do()", input, i) then DO
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else if startsWith ("don't()", input, i) then DONT
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else
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let
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val n1 = numberAt (i + 4) input
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val n2 = Option.mapPartial (fn n => numberAt (i + 5 + Substring.size n) input) n1
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in
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case (n1, n2) of
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(SOME(a), SOME(b)) =>
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if
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startsWith ("mul(", input, i) andalso
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String.sub (input, i + 4 + Substring.size a) = #"," andalso
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String.sub (input, i + 5 + Substring.size a + Substring.size b) = #")"
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then MUL (substrToInt a, substrToInt b) else NOOP
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| _ => NOOP
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end
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))
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val result = foldl (fn (ins, v) => case ins of MUL (a, b) => v + a + b | _ => v) 0 instructions
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