patrick
d94663ae0e
Blown way through my time budget and there's a bunch of low hanging fruit (data dependencies in LCM, for example) but I'm late for work. Co-authored-by: Smaug123 <patrick+github@patrickstevens.co.uk> Reviewed-on: #8
111 lines
3.1 KiB
Forth
111 lines
3.1 KiB
Forth
namespace AdventOfCode2023
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open System
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open System.Collections.Generic
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[<RequireQualifiedAccess>]
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module Day8 =
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type Instructions =
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{
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/// "true" is 'R'
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Steps : bool array
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Nodes : Dictionary<string, string * string>
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}
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let parse (s : string) =
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use mutable lines = StringSplitEnumerator.make '\n' s
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lines.MoveNext () |> ignore
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let stepsLine = lines.Current.TrimEnd ()
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let steps = Array.zeroCreate stepsLine.Length
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for i = 0 to stepsLine.Length - 1 do
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steps.[i] <- (stepsLine.[i] = 'R')
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let dict = Dictionary ()
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while lines.MoveNext () do
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if not lines.Current.IsEmpty then
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use mutable line = StringSplitEnumerator.make' ' ' lines.Current
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line.MoveNext () |> ignore
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let key = line.Current.ToString ()
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line.MoveNext () |> ignore
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line.MoveNext () |> ignore
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let v1 = line.Current.Slice(1, line.Current.Length - 2).ToString ()
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line.MoveNext () |> ignore
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let v2 = line.Current.Slice(0, line.Current.Length - 1).ToString ()
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dict.[key] <- (v1, v2)
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{
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Steps = steps
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Nodes = dict
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}
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let part1 (s : string) =
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let data = parse s
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let mutable i = 0
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let mutable currentNode = "AAA"
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let mutable answer = 0
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while currentNode <> "ZZZ" do
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let instruction = data.Nodes.[currentNode]
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if data.Steps.[i] then
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// "true" is R
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currentNode <- snd instruction
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else
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currentNode <- fst instruction
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i <- (i + 1) % data.Steps.Length
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answer <- answer + 1
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answer
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let inline lcm (periods : ^T[]) =
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let mutable lcm = periods.[0]
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let mutable i = 1
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while i < periods.Length do
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let euclid = Arithmetic.euclideanAlgorithm lcm periods.[i]
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lcm <- (lcm * periods.[i]) / euclid.Hcf
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i <- i + 1
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lcm
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let part2 (s : string) =
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let data = parse s
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let startingNodes = ResizeArray ()
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for key in data.Nodes.Keys do
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if key.[key.Length - 1] = 'A' then
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startingNodes.Add key
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let periods =
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Array.init
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startingNodes.Count
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(fun startNode ->
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let mutable i = 0
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let mutable currentNode = startingNodes.[startNode]
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let mutable answer = 0ul
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while currentNode.[currentNode.Length - 1] <> 'Z' do
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let instruction = data.Nodes.[currentNode]
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if data.Steps.[i] then
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// "true" is R
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currentNode <- snd instruction
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else
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currentNode <- fst instruction
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i <- (i + 1) % data.Steps.Length
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answer <- answer + 1ul
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uint64 answer
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)
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lcm periods
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