From b95d404ee6df9ae95a4ff214b376b3509568277e Mon Sep 17 00:00:00 2001
From: Brian Chu <brianmchu42@gmail.com>
Date: Thu, 6 Jan 2022 12:25:42 -0800
Subject: solution for day 12

---
 day12.fsx | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 day12.fsx

diff --git a/day12.fsx b/day12.fsx
new file mode 100644
index 0000000..17bcc6b
--- /dev/null
+++ b/day12.fsx
@@ -0,0 +1,66 @@
+open System.IO
+
+type Reg = string
+type Lit = int
+type Value =
+    | LiteralVal of literal: Lit
+    | Register of register: Reg
+
+type Instruction =
+    | Cpy of copied: Value * register: Reg
+    | Inc of register: Reg
+    | Dec of register: Reg
+    | Jnz of compared: Value * offset: Lit
+
+let parseInstruction (line:string): Instruction =
+    let split = line.Split " "
+    match split[0] with
+    | "inc" -> Inc split[1]
+    | "dec" -> Dec split[1]
+    | "cpy" ->
+        let mutable parsed = 0
+        if (System.Int32.TryParse(split[1], &parsed))
+        then Cpy (LiteralVal parsed, split[2])
+        else Cpy (Register split[1], split[2])
+    | "jnz" -> 
+        let mutable parsed = 0
+        if (System.Int32.TryParse(split[1], &parsed))
+        then Jnz (LiteralVal parsed, (int split[2]))
+        else Jnz (Register split[1], (int split[2]))
+    | _ -> Inc ""
+
+let rec execute index insts registers =
+    if index < 0 || index > (Array.length insts) - 1
+    then 
+        Map.find "a" registers
+    else
+        match insts[index] with
+        | Cpy (value, reg) -> 
+            let copied =
+                match value with
+                | LiteralVal num -> num
+                | Register reg -> Map.find reg registers
+            let newRegisters = Map.change reg (function | Some x -> Some copied | None -> None) registers
+            execute (index + 1) insts newRegisters
+        | Inc reg ->
+            let newRegisters = Map.change reg (function | Some x -> Some (x + 1) | None -> None) registers
+            execute (index + 1) insts newRegisters
+        | Dec reg ->
+            let newRegisters = Map.change reg (function | Some x -> Some (x - 1) | None -> None) registers
+            execute (index + 1) insts newRegisters
+        | Jnz (reg, offset) ->
+            let compared =
+                match reg with
+                | LiteralVal num -> num
+                | Register reg -> Map.find reg registers
+            if compared <> 0
+            then 
+                execute (index + offset) insts registers
+            else
+                execute (index + 1) insts registers
+    
+let lines = File.ReadAllLines "day12.txt" |> Array.map parseInstruction
+let regsPart1: Map<string, Lit> = Map.ofList [("a", 0); ("b", 0); ("c", 0); ("d", 0)]
+execute 0 lines regsPart1 |> printfn "%d"
+let regsPart2: Map<string, Lit> = Map.ofList [("a", 0); ("b", 0); ("c", 1); ("d", 0)]
+execute 0 lines regsPart2 |> printfn "%d"
\ No newline at end of file
-- 
cgit 1.4.1-2-gfad0