1 files changed, 84 insertions, 0 deletions
diff --git a/day23.fsx b/day23.fsx
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+++ b/day23.fsx
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+open System.IO
+open System.Collections.Generic
+open System.Text.RegularExpressions
+
+type Register = string
+type Value =
+    | Literal of int64
+    | Reg of Register
+
+let (|InstRegex|_|) pattern string =
+    let m = Regex(pattern).Match(string)
+    if m.Success then
+        Some(List.tail [for g in m.Groups -> g.Value])
+    else None
+
+type Instruction =
+    | Set of x: Register * y: Value
+    | Sub of x: Register * y: Value
+    | Mul of x: Register * y: Value
+    | Jnz of x: Value * y: Value
+
+let resolveValue (value: Value) (registers: Dictionary<string, int64> ) =
+    let tryGetDefaultRegister key =
+        if not (registers.ContainsKey(key)) then registers.[key] <- 0L
+        registers.[key]
+ 
+    match value with
+    | Literal x -> x
+    | Reg x -> tryGetDefaultRegister x
+
+let parseValue line =
+    match line with
+    | InstRegex "set ([a-p]) ([a-p])" [x; y]   -> Set (x, Reg y)
+    | InstRegex "set ([a-p]) (-?\d+)" [x; y]   -> Set (x, Literal (int y))
+    | InstRegex "sub ([a-p]) ([a-p])" [x; y]   -> Sub (x, Reg y)
+    | InstRegex "sub ([a-p]) (-?\d+)" [x; y]   -> Sub (x, Literal (int y))
+    | InstRegex "mul ([a-p]) ([a-p])" [x; y]   -> Mul (x, Reg y)
+    | InstRegex "mul ([a-p]) (-?\d+)" [x; y]   -> Mul (x, Literal (int y))
+    | InstRegex "jnz ([a-p]) ([a-p])" [x; y]   -> Jnz (Reg x, Reg y)
+    | InstRegex "jnz ([a-p]) (-?\d+)" [x; y]   -> Jnz (Reg x, Literal (int y))
+    | InstRegex "jnz (-?\d+) ([a-p])" [x; y]   -> Jnz (Literal (int x), Reg y)
+    | InstRegex "jnz (-?\d+) (-?\d+)" [x; y]   -> Jnz (Literal (int x), Literal (int y))
+    | x -> printfn "%A" x; failwith "invalid input"
+
+let rec executeInst (instructions: Instruction array) (registers: Dictionary<string, int64>) (index: int64) mulCount =
+    if (int index) >= Array.length instructions || (int index) < 0 then mulCount
+    else
+    match instructions.[int index] with
+    | Set(x, y) -> 
+        if not (registers.ContainsKey(x)) then registers.[x] <- 0
+        registers.[x] <- resolveValue y registers
+        executeInst instructions registers (index + 1L) mulCount
+    | Sub(x, y) ->
+        if not (registers.ContainsKey(x)) then registers.[x] <- 0
+        registers.[x] <- registers.[x] - resolveValue y registers
+        executeInst instructions registers (index + 1L) mulCount
+    | Mul(x, y) -> 
+        if not (registers.ContainsKey(x)) then registers.[x] <- 0
+        registers.[x] <- registers.[x] * resolveValue y registers
+        executeInst instructions registers (index + 1L) (mulCount + 1)
+    | Jnz(x, y) ->
+        if (resolveValue x registers) <> 0 then
+            executeInst instructions registers (index + resolveValue y registers) mulCount
+        else
+            executeInst instructions registers (index + 1L) mulCount
+
+let part1() =
+    let registers = new Dictionary<string, int64>()
+    let input = File.ReadAllLines "day23.txt" |> Array.map parseValue
+    let mulCount = executeInst input registers 0 0
+    printfn "%A" mulCount
+
+// i knew it couldn't be that easy :(
+// time to decompile the assembly and figure out what's happening
+
+// let part2() = 
+//     let registers = new Dictionary<string, int64>()
+//     registers.["a"] <- 1
+//     let input = File.ReadAllLines "day23.txt" |> Array.map parseValue
+//     executeInst input registers 0 0 |> ignore
+//     printfn "%A" registers.["h"]
+
+let () =
+    part1()
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