Day 8 part 1

AdventOfCode2023.FSharp/AdventOfCode2023.FSharp.Lib/Day8.fs

@@ -1,30 +1,67 @@
 namespace AdventOfCode2023
 
 open System
+open System.Collections.Generic
 open System.Globalization
 
 [<RequireQualifiedAccess>]
 module Day8 =
 
-    let parse (s : string) : ResizeArray<int> =
+    type Instructions =
+        {
+            /// "true" is 'R'
+            Steps : bool array
+
+            Nodes : Dictionary<string, string * string>
+        }
+
+    let parse (s : string) =
         use mutable lines = StringSplitEnumerator.make '\n' s
-        let result = ResizeArray ()
+
+        lines.MoveNext () |> ignore
+
+        let stepsLine = lines.Current.TrimEnd()
+        let steps = Array.zeroCreate stepsLine.Length
+        for i = 0 to stepsLine.Length - 1 do
+            steps.[i] <- (stepsLine.[i] = 'R')
+
+        let dict = Dictionary ()
 
         while lines.MoveNext () do
             if not lines.Current.IsEmpty then
                 use mutable line = StringSplitEnumerator.make' ' ' lines.Current
                 line.MoveNext () |> ignore
-                result.Add (3)
+                let key = line.Current.ToString ()
+                line.MoveNext () |> ignore
+                line.MoveNext () |> ignore
+                let v1 = line.Current.Slice(1, line.Current.Length - 2).ToString ()
+                line.MoveNext () |> ignore
+                let v2 = line.Current.Slice(0, line.Current.Length - 1).ToString ()
+                dict.[key] <- (v1, v2)
 
-        result
+        {
+            Steps = steps
+            Nodes = dict
+        }
 
     let part1 (s : string) =
-        let arr = parse s
+        let data = parse s
+        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 part2 (s : string) =
-        let arr = parse s
+        let data = parse s
         let mutable answer = 0
 
         answer