2 files changed, 67 insertions, 0 deletions
diff --git a/aoc-2022-dotnet/Common/Util.fs b/aoc-2022-dotnet/Common/Util.fs
index 568f2c2..ac5d981 100644
--- a/aoc-2022-dotnet/Common/Util.fs
+++ b/aoc-2022-dotnet/Common/Util.fs
@@ -65,6 +65,21 @@ module Util =
         | h :: t -> h, t @ [ h ]
         | [] -> failwith "Empty list!"
 
+    let tsort graph =
+        let dfs =
+            let rec explore path result node =
+                if List.contains node path then
+                    failwith "Cycle found!"
+                elif List.contains node result then
+                    result
+                else
+                    node
+                    :: List.fold (explore (node :: path)) result (Map.find node graph)
+
+            explore []
+
+        graph |> Map.keys |> Seq.fold dfs [] |> List.rev
+
     let topN n xs =
         Seq.fold
             (fun acc x ->
diff --git a/aoc-2022-dotnet/Day21/Program.fs b/aoc-2022-dotnet/Day21/Program.fs
index e5d8920..3837054 100644
--- a/aoc-2022-dotnet/Day21/Program.fs
+++ b/aoc-2022-dotnet/Day21/Program.fs
@@ -1,9 +1,61 @@
 module Day21
 
 open System.IO
+open FSharpPlus
 open FParsec
 open Common
 
+type MonkeyName = string
+type Operator = int64 -> int64 -> int64
+
+type MonkeyJob =
+    | Number of int64
+    | Operation of MonkeyName * Operator * MonkeyName
+
+    static member dependencies =
+        function
+        | Number _ -> []
+        | Operation (l, _, r) -> [ l; r ]
+
+type Monkey = MonkeyName * MonkeyJob
+
+let charToOperator =
+    function
+    | '+' -> (+)
+    | '-' -> (-)
+    | '*' -> (*)
+    | '/' -> (/)
+    | c -> failwithf "Invalid operator: %c" c
+
+let parseMonkey =
+    let pspc = pchar ' '
+    let pname = anyString 4 |>> MonkeyName
+    let poper = pspc >>. anyChar .>> pspc |>> charToOperator
+    let pnumber = pint64 |>> Number
+    let poperation = tuple3 pname poper pname |>> Operation
+    let pjob = pnumber <|> poperation
+    let pmonkey = pname .>> pstring ": " .>>. pjob |>> Monkey
+    Util.parse pmonkey
+
+let solution input =
+    let monkeys = input |> Seq.map parseMonkey |> Map.ofSeq
+
+    monkeys
+    |> Map.mapValues MonkeyJob.dependencies
+    |> Util.tsort
+    |> List.fold
+        (fun values name ->
+            Map.add
+                name
+                (match monkeys[name] with
+                 | Number num -> num
+                 | Operation (left, operator, right) -> operator values[left] values[right])
+                values)
+        Map.empty
+    |> Map.find "root"
+
 let test = File.ReadLines("test.txt")
+assert (solution test = 152)
 
 let input = File.ReadLines("input.txt")
+printfn "%d" <| solution input