diff --git a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj
index 2b11007..73ba81f 100644
--- a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj
+++ b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/AdventOfCode2023.FSharp.Lib.fsproj
@@ -9,6 +9,7 @@
+
diff --git a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Arithmetic.fs b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Arithmetic.fs
new file mode 100644
index 0000000..d2725de
--- /dev/null
+++ b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Arithmetic.fs
@@ -0,0 +1,67 @@
+namespace AdventOfCode2023
+
+[]
+module Arithmetic =
+
+ /// Compute floor(sqrt(i)).
+ let inline sqrt (i : ^a) =
+ if i <= LanguagePrimitives.GenericOne then
+ i
+ else
+ let rec go start =
+ let next = start + LanguagePrimitives.GenericOne
+ let sqr = next * next
+
+ if sqr < LanguagePrimitives.GenericZero then
+ // Overflow attempted, so the sqrt is between start and next
+ start
+ elif i < sqr then
+ start
+ elif i = sqr then
+ next
+ else
+ go next
+
+ go LanguagePrimitives.GenericOne
+
+ /// Find Hcf, A, B s.t. A * a + B * b = Hcf, and Hcf is the highest common factor of a and b.
+ let inline euclideanAlgorithm
+ (a : ^a)
+ (b : ^a)
+ : {|
+ Hcf : ^a
+ A : ^a
+ B : ^a
+ |}
+ =
+ let rec go rMin1 r sMin1 s tMin1 t =
+ if r = LanguagePrimitives.GenericZero then
+ {|
+ Hcf = rMin1
+ A = sMin1
+ B = tMin1
+ |}
+ else
+ let newQ = rMin1 / r
+ go r (rMin1 - newQ * r) s (sMin1 - newQ * s) t (tMin1 - newQ * t)
+
+ let maxA = max a b
+ let minB = min a b
+
+ let result =
+ go
+ maxA
+ minB
+ LanguagePrimitives.GenericOne
+ LanguagePrimitives.GenericZero
+ LanguagePrimitives.GenericZero
+ LanguagePrimitives.GenericOne
+
+ if a = maxA then
+ result
+ else
+ {|
+ Hcf = result.Hcf
+ A = result.B
+ B = result.A
+ |}
diff --git a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day8.fs b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day8.fs
index f22d52c..43a17b9 100644
--- a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day8.fs
+++ b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day8.fs
@@ -2,7 +2,6 @@ namespace AdventOfCode2023
open System
open System.Collections.Generic
-open System.Globalization
[]
module Day8 =
@@ -20,8 +19,9 @@ module Day8 =
lines.MoveNext () |> ignore
- let stepsLine = lines.Current.TrimEnd()
+ let stepsLine = lines.Current.TrimEnd ()
let steps = Array.zeroCreate stepsLine.Length
+
for i = 0 to stepsLine.Length - 1 do
steps.[i] <- (stepsLine.[i] = 'R')
@@ -49,19 +49,60 @@ module Day8 =
let mutable i = 0
let mutable currentNode = "AAA"
let mutable answer = 0
+
while currentNode <> "ZZZ" do
let instruction = data.Nodes.[currentNode]
+
if data.Steps.[i] then
// "true" is R
currentNode <- snd instruction
else
currentNode <- fst instruction
+
i <- (i + 1) % data.Steps.Length
answer <- answer + 1
+
answer
+ let inline lcm (periods : ^T[]) =
+ let mutable lcm = periods.[0]
+ let mutable i = 1
+
+ while i < periods.Length do
+ let euclid = Arithmetic.euclideanAlgorithm lcm periods.[i]
+ lcm <- (lcm * periods.[i]) / euclid.Hcf
+ i <- i + 1
+
+ lcm
+
let part2 (s : string) =
let data = parse s
- let mutable answer = 0
- answer
+ let startingNodes =
+ data.Nodes.Keys
+ |> Seq.choose (fun k -> if k.[k.Length - 1] = 'A' then Some k else None)
+ |> Seq.toArray
+
+ let periods =
+ startingNodes
+ |> Array.map (fun startNode ->
+ let mutable i = 0
+ let mutable currentNode = startNode
+ let mutable answer = 0ul
+
+ while currentNode.[currentNode.Length - 1] <> 'Z' do
+ let instruction = data.Nodes.[currentNode]
+
+ if data.Steps.[i] then
+ // "true" is R
+ currentNode <- snd instruction
+ else
+ currentNode <- fst instruction
+
+ i <- (i + 1) % data.Steps.Length
+ answer <- answer + 1ul
+
+ uint64 answer
+ )
+
+ lcm periods
diff --git a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs
index 5514ffb..01889d6 100644
--- a/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs
+++ b/AdventOfCode2023.FSharp/AdventOfCode2023.FSharp/Program.fs
@@ -161,13 +161,18 @@ module Program =
Console.WriteLine "=====Day 8====="
do
- let input = Path.Combine (dir.FullName, "day8.txt") |> File.ReadAllText
+ let input =
+ try
+ Path.Combine (dir.FullName, "day8part1.txt") |> File.ReadAllText
+ with :? FileNotFoundException ->
+ Path.Combine (dir.FullName, "day8.txt") |> File.ReadAllText
sw.Restart ()
let part1 = Day8.part1 input
sw.Stop ()
Console.WriteLine (part1.ToString ())
Console.Error.WriteLine ((1_000.0 * float sw.ElapsedTicks / float Stopwatch.Frequency).ToString () + "ms")
sw.Restart ()
+ let input = Path.Combine (dir.FullName, "day8.txt") |> File.ReadAllText
let part2 = Day8.part2 input
sw.Stop ()
Console.WriteLine (part2.ToString ())
diff --git a/AdventOfCode2023.FSharp/Test/Test.fsproj b/AdventOfCode2023.FSharp/Test/Test.fsproj
index 43e52b8..9a4c538 100644
--- a/AdventOfCode2023.FSharp/Test/Test.fsproj
+++ b/AdventOfCode2023.FSharp/Test/Test.fsproj
@@ -25,6 +25,7 @@
+
diff --git a/AdventOfCode2023.FSharp/Test/TestDay8.fs b/AdventOfCode2023.FSharp/Test/TestDay8.fs
index 794869a..84f7b10 100644
--- a/AdventOfCode2023.FSharp/Test/TestDay8.fs
+++ b/AdventOfCode2023.FSharp/Test/TestDay8.fs
@@ -1,6 +1,5 @@
namespace AdventOfCode2023.Test
-open System
open AdventOfCode2023
open NUnit.Framework
open FsUnitTyped
@@ -9,11 +8,11 @@ open System.IO
[]
module TestDay8 =
- let sample = Assembly.getEmbeddedResource typeof.Assembly "day8.txt"
-
[]
let part1Sample () =
- sample |> Day8.part1 |> shouldEqual 2
+ Assembly.getEmbeddedResource typeof.Assembly "day8part1.txt"
+ |> Day8.part1
+ |> shouldEqual 2
[]
let part1Sample2 () =
@@ -22,11 +21,14 @@ module TestDay8 =
AAA = (BBB, BBB)
BBB = (AAA, ZZZ)
ZZZ = (ZZZ, ZZZ)"""
- |> Day8.part1 |> shouldEqual 6
+ |> Day8.part1
+ |> shouldEqual 6
[]
let part2Sample () =
- sample |> Day8.part2 |> shouldEqual 0
+ Assembly.getEmbeddedResource typeof.Assembly "day8.txt"
+ |> Day8.part2
+ |> shouldEqual 6uL
[]
let part1Actual () =
@@ -39,7 +41,7 @@ ZZZ = (ZZZ, ZZZ)"""
Assert.Inconclusive ()
failwith "unreachable"
- Day8.part1 s |> shouldEqual 0
+ Day8.part1 s |> shouldEqual 19199
[]
let part2Actual () =
@@ -52,4 +54,4 @@ ZZZ = (ZZZ, ZZZ)"""
Assert.Inconclusive ()
failwith "unreachable"
- Day8.part2 s |> shouldEqual 0
+ Day8.part2 s |> shouldEqual 13663968099527uL
diff --git a/AdventOfCode2023.FSharp/Test/samples/day8.txt b/AdventOfCode2023.FSharp/Test/samples/day8.txt
index 9029a1b..5b3fa58 100644
--- a/AdventOfCode2023.FSharp/Test/samples/day8.txt
+++ b/AdventOfCode2023.FSharp/Test/samples/day8.txt
@@ -1,9 +1,10 @@
-RL
+LR
-AAA = (BBB, CCC)
-BBB = (DDD, EEE)
-CCC = (ZZZ, GGG)
-DDD = (DDD, DDD)
-EEE = (EEE, EEE)
-GGG = (GGG, GGG)
-ZZZ = (ZZZ, ZZZ)
+11A = (11B, XXX)
+11B = (XXX, 11Z)
+11Z = (11B, XXX)
+22A = (22B, XXX)
+22B = (22C, 22C)
+22C = (22Z, 22Z)
+22Z = (22B, 22B)
+XXX = (XXX, XXX)
diff --git a/AdventOfCode2023.FSharp/Test/samples/day8part1.txt b/AdventOfCode2023.FSharp/Test/samples/day8part1.txt
new file mode 100644
index 0000000..9029a1b
--- /dev/null
+++ b/AdventOfCode2023.FSharp/Test/samples/day8part1.txt
@@ -0,0 +1,9 @@
+RL
+
+AAA = (BBB, CCC)
+BBB = (DDD, EEE)
+CCC = (ZZZ, GGG)
+DDD = (DDD, DDD)
+EEE = (EEE, EEE)
+GGG = (GGG, GGG)
+ZZZ = (ZZZ, ZZZ)