solution for day 5

2 files changed, 63 insertions, 0 deletions

diff --git a/Program.fs b/Program.fs
index 7a64584..de1421b 100644
--- a/Program.fs
+++ b/Program.fs
@@ -16,5 +16,7 @@ match (day, part) with
 | (3, 2) -> Day3.part2 () |> printf "%A\n"
 | (4, 1) -> Day4.part1 () |> printf "%A\n"
 | (4, 2) -> Day4.part2 () |> printf "%A\n"
+| (5, 1) -> Day5.part1 () |> printf "%A\n"
+| (5, 2) -> Day5.part2 () |> printf "%A\n"
 | (x, y) when (1 <= x && x <= 25) && (y = 1 || y = 2)  -> raise (NotImplemented("not implemented yet"))
 | _ -> raise (NotImplemented("invalid values"))
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diff --git a/solutions/day5.fs b/solutions/day5.fs
new file mode 100644
index 0000000..6c8bce3
--- /dev/null
+++ b/solutions/day5.fs
@@ -0,0 +1,61 @@
+namespace Solutions
+
+module Day5 =
+    open System.IO
+    open System.Text.RegularExpressions
+
+    // forgive me lord for what i'm about to do
+    // too lazy to figure out how to parse initial state so hardcoding instead
+    let initState = [|
+                    ['D'; 'T'; 'W'; 'N'; 'L']; 
+                    ['H'; 'P'; 'C'];
+                    ['J'; 'M'; 'G'; 'D'; 'N'; 'H'; 'P'; 'W'];
+                    ['L'; 'Q'; 'T'; 'N'; 'S'; 'W'; 'C'];
+                    ['N'; 'C'; 'H'; 'P'];
+                    ['B'; 'Q'; 'W'; 'M'; 'D'; 'N'; 'H'; 'T'];
+                    ['L'; 'S'; 'G'; 'J'; 'R'; 'B'; 'M'];
+                    ['T'; 'R'; 'B'; 'V'; 'G'; 'W'; 'N'; 'Z'];
+                    ['L'; 'P'; 'N'; 'D'; 'G'; 'W'] 
+                    |]
+
+    type instruction = {
+        amount: int;
+        source: int;
+        target: int
+    }
+
+    let getInstruction inst =
+        let matches = Regex.Matches(inst, "move (\d+) from (\d+) to (\d+)")
+                        |> Seq.head
+                        |> fun x -> x.Groups
+                        |> List.ofSeq |> List.tail
+                        |> List.map (fun x -> int x.Value)
+        assert (List.length matches = 3)
+        {amount = matches[0]; source = matches[1] - 1; target = matches[2] - 1}
+    
+    let instructions = File.ReadLines("inputs/day5.txt") 
+                        |> Array.ofSeq 
+                        |> fun x -> Array.splitAt (Array.findIndex ((=) "") x) x
+                        |> snd |> Array.tail |> Array.map getInstruction
+
+    let executeInstruction1 (state: list<char>[]) inst =
+        for _ in 1..inst.amount do
+            match state[inst.source] with
+            | top::bottom ->
+                state[inst.source] <- bottom
+                state[inst.target] <- top::state[inst.target]
+            | _ -> failwith "this shouldn't happen"
+
+    let part1 () = 
+        let mutable currentState = initState
+        Array.iter (executeInstruction1 currentState) instructions
+        Array.map (List.head >> string) currentState |> String.concat ""
+
+    let executeInstruction2 (state: char [] []) inst =
+        state[inst.target] <- Array.append state[inst.source].[..inst.amount-1] state[inst.target]
+        state[inst.source] <- state[inst.source][inst.amount..]
+        
+    let part2 () = 
+        let mutable currentState = initState |> Array.map Array.ofList
+        Array.iter (executeInstruction2 currentState) instructions
+        Array.map (Array.head >> string) currentState |> String.concat ""
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