From 39551c066cba5c4fae8c9131568a6b6db45cdcba Mon Sep 17 00:00:00 2001
From: Malachy Byrne <malachybyrne1@gmail.com>
Date: Tue, 2 Dec 2025 20:10:20 +0000
Subject: [PATCH] Add day 2

---
 advent-of-code/Program.fs           | 10 ++++---
 advent-of-code/tasks/day-2/Star1.fs | 24 +++++++++++++++++
 advent-of-code/tasks/day-2/Star2.fs | 41 +++++++++++++++++++++++++++++
 3 files changed, 72 insertions(+), 3 deletions(-)
 create mode 100644 advent-of-code/tasks/day-2/Star1.fs
 create mode 100644 advent-of-code/tasks/day-2/Star2.fs

diff --git a/advent-of-code/Program.fs b/advent-of-code/Program.fs
index a77ede8..6f3350e 100644
--- a/advent-of-code/Program.fs
+++ b/advent-of-code/Program.fs
@@ -1,11 +1,15 @@
 module advent_of_code.Program
 
-open advent_of_code.tasks.day_1
+open advent_of_code.tasks
 
 [<EntryPoint>]
 let main _ =
-    let _, day1Star1 = Star1.main 50 0
+    let _, day1Star1 = day_1.Star1.main 50 0
     printfn $"{day1Star1}"
-    let _, day1Star2 = Star2.main 50 0
+    let _, day1Star2 = day_1.Star2.main 50 0
     printfn $"{day1Star2}"
+    let day2Star1 = day_2.Star1.main
+    printfn $"{day2Star1}"
+    let day2Star2 = day_2.Star2.main
+    printfn $"{day2Star2}"
     0
diff --git a/advent-of-code/tasks/day-2/Star1.fs b/advent-of-code/tasks/day-2/Star1.fs
new file mode 100644
index 0000000..b4638dd
--- /dev/null
+++ b/advent-of-code/tasks/day-2/Star1.fs
@@ -0,0 +1,24 @@
+module advent_of_code.tasks.day_2.Star1
+
+open System.IO
+
+let stream = new StreamReader("tasks/day-2/input.txt")
+
+let convertToString (i: int64) = i |> string
+
+let isInvalid (id: string) =
+    let individualCount = id.Length / 2
+    let firstHalf, secondHalf = id[0..individualCount - 1], id[individualCount..]
+    if firstHalf = secondHalf then id |> int64 else 0
+
+let rec getInvalid (lines: string list) =
+    let line, tail = lines.Head, lines.Tail
+    let els = line.Split("-")
+    let low, high = els[0] |> int64, els[1] |> int64
+    let invalids = [low .. high] |> List.map convertToString |> List.map isInvalid
+
+    List.sum invalids + if tail.IsEmpty then 0 |> int64 else getInvalid tail
+
+let main =
+    let lines = stream.ReadLine().Split(",") |> Array.toList
+    getInvalid lines
diff --git a/advent-of-code/tasks/day-2/Star2.fs b/advent-of-code/tasks/day-2/Star2.fs
new file mode 100644
index 0000000..cb1a893
--- /dev/null
+++ b/advent-of-code/tasks/day-2/Star2.fs
@@ -0,0 +1,41 @@
+module advent_of_code.tasks.day_2.Star2
+
+open System.IO
+
+let stream = new StreamReader("tasks/day-2/input.txt")
+
+let convertToString (i: int64) = i |> string
+
+let divideString (str: string) (n: int) =
+    let count = str.Length / n
+    let mutable parts = Set.empty
+    for i in 0 .. count - 1 do
+        let start = i * n
+        parts <- parts.Add(str.Substring(start, n))
+    parts
+
+let rec isInvalid (id: string) (chars: int) =
+    let biggerSlices = if chars = id.Length then 0 |> int64 else isInvalid id (chars + 1)
+    if (chars = id.Length) then
+        0
+    else if (biggerSlices <> 0) then
+        biggerSlices
+    else if (id.Length % chars <> 0) then
+        0
+    else
+        let parts = divideString id chars
+        if parts.Count = 1 then id |> int64 else 0
+
+let checkValid (id: string) = isInvalid id 1
+
+let rec getInvalid (lines: string list) =
+    let line, tail = lines.Head, lines.Tail
+    let els = line.Split("-")
+    let low, high = els[0] |> int64, els[1] |> int64
+    let invalids = [low .. high] |> List.map convertToString |> List.map checkValid
+
+    List.sum invalids + if tail.IsEmpty then 0 |> int64 else getInvalid tail
+
+let main =
+    let lines = stream.ReadLine().Split(",") |> Array.toList
+    getInvalid lines