31 lines
1.0 KiB
Standard ML
31 lines
1.0 KiB
Standard ML
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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 substrToInt (n : substring) = valOf (Int.fromString (Substring.string n))
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fun sum (l : int list) : int = foldl (op +) 0 l
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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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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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if isSome n1 andalso isSome n2 andalso
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String.substring (input, i, 4) = "mul(" andalso
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String.sub (input, i + 4 + Substring.size (valOf n1)) = #"," andalso
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String.sub (input, i + 5 + Substring.size (valOf n1) + Substring.size (valOf n2)) = #")"
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then SOME (n1, n2) else NONE
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end))
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val instructions = List.mapPartial
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(fn (num) => case num of SOME (SOME x, SOME y) => SOME (substrToInt x, substrToInt y) | _ => NONE)
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instructions
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val result = sum (map (op *) instructions)
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