39 lines
831 B
Scala
39 lines
831 B
Scala
package aoc.day9
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import aoc._
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object Parser extends CommonParser:
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val nums = rep1(long)
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val lns = lines.toSeq
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val inputs = lns.map(Parser.parse(Parser.nums, _).get).toSeq
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// part1
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def calculate(add: Int => (Long, Seq[Long]) => Long)(ns: Seq[Long]) =
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@scala.annotation.tailrec
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def loop(ns: Seq[Long], depth: Int, sum: Long): Long =
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if ns.forall(_ == 0) then sum
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else
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val diff = ns.tail.lazyZip(ns).map(_ - _)
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loop(diff, depth + 1, add(depth)(sum, ns))
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loop(ns, 0, 0)
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def part1 =
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println(inputs.map(calculate(_ => (sum, ns) => sum + ns.last)).sum)
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// part 2
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def part2 =
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println(
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inputs
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.map(
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calculate(depth => (sum, ns) => sum + ns.head * (if depth % 2 == 0 then 1 else -1))
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)
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.sum
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)
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@main def Day9(part: Int) = part match
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case 1 => part1
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case 2 => part2
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