From 306af61cdd23ebf80f38c1947a806de39123f4ba Mon Sep 17 00:00:00 2001
From: =?utf8?q?Gr=C3=A9gory=20Burri?= <gregory.burri@matisa.ch>
Date: Wed, 5 Dec 2018 13:48:30 +0100
Subject: [PATCH] A shorter day 5 solution.

---
 Day05.fs             | 19 +++++++++----------
 Program.fs           |  2 +-
 Tests/Day05 tests.fs |  8 ++++----
 3 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/Day05.fs b/Day05.fs
index accb3f9..a752d91 100644
--- a/Day05.fs
+++ b/Day05.fs
@@ -2,20 +2,19 @@ module AdventOfCode2018.Day05
 
 open System
 
-let diffMajMin = int 'A' - int 'a'
+let diffMajMin = int 'a' - int 'A'
 
-let reduce (polymer : string) : string =
-    Seq.foldBack (
+let reduce (polymer : char list) : char list =
+    List.foldBack (
         fun a result ->
             match result with
             | b :: rest when int a - int b |> abs = diffMajMin -> rest
             | _ -> a :: result
     ) polymer [ ]
-    |> Array.ofList
-    |> String.Concat
 
-let findShortestPolymer (polymer : string) : string =
-    polymer.ToLower()
-    |> Seq.distinct
-    |> Seq.map (fun unit -> polymer.Replace(string unit, "", StringComparison.InvariantCultureIgnoreCase) |> reduce)
-    |> Seq.minBy String.length
+let findShortestPolymer (polymer : char list) : char list =
+    polymer
+    |> List.map Char.ToLower
+    |> List.distinct
+    |> List.map (fun unit -> polymer |> List.filter (fun c -> Char.ToLower c <> unit) |> reduce)
+    |> List.minBy List.length
diff --git a/Program.fs b/Program.fs
index 2ff2dd3..fb433b7 100644
--- a/Program.fs
+++ b/Program.fs
@@ -22,7 +22,7 @@ let day04 () =
     sprintf "part1 = %A, part2 = %A" (sleepestGuardId * sleepestTime) (sleepestGuardIdSameTime * sleepestTimeSameTime)
 
 let day05 () =
-    let reduced = (File.ReadAllText "Data/day05.input").Trim () |> Day05.reduce
+    let reduced = (File.ReadAllText "Data/day05.input").Trim () |> List.ofSeq |> Day05.reduce
     sprintf "part1 = %A, part2 = %A" reduced.Length (Day05.findShortestPolymer reduced).Length
 
 let days : Map<int, unit -> string> =
diff --git a/Tests/Day05 tests.fs b/Tests/Day05 tests.fs
index 6c47069..560db29 100644
--- a/Tests/Day05 tests.fs	
+++ b/Tests/Day05 tests.fs	
@@ -12,11 +12,11 @@ type ``Day05 tests`` (output : ITestOutputHelper) =
 
     [<Fact>]
     let ``(Part1) From web page`` () =
-        let input = "dabAcCaCBAcCcaDA"
-        Day05.reduce input =! "dabCBAcaDA"
+        let input = List.ofSeq "dabAcCaCBAcCcaDA"
+        Day05.reduce input =! List.ofSeq "dabCBAcaDA"
 
     [<Fact>]
     let ``(Part2) From web page`` () =
-        let input = "dabAcCaCBAcCcaDA"
-        Day05.findShortestPolymer input =! "daDA"
+        let input = List.ofSeq "dabAcCaCBAcCcaDA"
+        Day05.findShortestPolymer input =! List.ofSeq "daDA"
 
-- 
2.45.2