From c629e2e3694ab207df9de2b4198171325a3b61e5 Mon Sep 17 00:00:00 2001
From: Ummon <greg.burri@gmail.com>
Date: Wed, 6 Dec 2017 09:41:48 +0100
Subject: [PATCH] Reduce execution time from 1s to 0.1s for day 6

---
 AdventOfCode2017.sln        |  8 +++++++-
 AdventOfCode2017/Day6.fs    | 17 ++++++++++++++++-
 AdventOfCode2017/Program.fs |  4 +++-
 3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/AdventOfCode2017.sln b/AdventOfCode2017.sln
index b07e76f..bc9b5dc 100644
--- a/AdventOfCode2017.sln
+++ b/AdventOfCode2017.sln
@@ -1,7 +1,7 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
-VisualStudioVersion = 15.0.27004.2010
+VisualStudioVersion = 15.0.27130.0
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "AdventOfCode2017", "AdventOfCode2017\AdventOfCode2017.fsproj", "{D3555943-8102-43D1-B3CB-570A4E4EC513}"
 EndProject
@@ -14,6 +14,9 @@ EndProject
 Project("{F2A71F9B-5D33-465A-A702-920D77279786}") = "Tests", "Tests\Tests.fsproj", "{238BFFBE-E2D4-4DC4-804C-6E43205E4701}"
 EndProject
 Global
+	GlobalSection(Performance) = preSolution
+		HasPerformanceSessions = true
+	EndGlobalSection
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
 		Release|Any CPU = Release|Any CPU
@@ -34,4 +37,7 @@ Global
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {1DAC18E9-E52B-45B9-AB96-686277B1EB81}
 	EndGlobalSection
+	GlobalSection(Performance) = preSolution
+		HasPerformanceSessions = true
+	EndGlobalSection
 EndGlobal
diff --git a/AdventOfCode2017/Day6.fs b/AdventOfCode2017/Day6.fs
index 85fac4c..867d408 100644
--- a/AdventOfCode2017/Day6.fs
+++ b/AdventOfCode2017/Day6.fs
@@ -1,12 +1,27 @@
 module AdventOfCode2017.Day6
 
 open System
+open System.Linq
 
 type Blocks = int[]
 
 let parseInput (str : string) : int[] =
     str.Split ([| '\r'; '\t'; ' ' |], StringSplitOptions.RemoveEmptyEntries) |> Array.map int
 
+// Custom equality: more efficient than '='.
+let inline (|=|) (a1 : 'a[]) (a2 : 'a[]) : bool =
+    if a1.Length <> a2.Length then
+        false
+    else
+        let rec result i =
+            if i = a1.Length then
+                true
+            elif a1.[i] <> a2.[i] then
+                false
+            else
+                result (i + 1)
+        result 0
+
 let nbRedistribution (blocks : Blocks) =
     let rec next (previous : Blocks list) =
         let blocks = List.head previous |> Array.copy
@@ -16,7 +31,7 @@ let nbRedistribution (blocks : Blocks) =
             let i' = offset % blocks.Length
             blocks.[i'] <- blocks.[i'] + 1
 
-        match previous |> List.tryFindIndex ((=) blocks) with
+        match previous |> List.tryFindIndex ((|=|) blocks) with
         | Some i -> previous, i + 1
         | None -> next (blocks :: previous)
 
diff --git a/AdventOfCode2017/Program.fs b/AdventOfCode2017/Program.fs
index b5116bb..e64ecf4 100644
--- a/AdventOfCode2017/Program.fs
+++ b/AdventOfCode2017/Program.fs
@@ -29,6 +29,8 @@ let day6 () =
     sprintf "part1 = %A, part2 = %A" part1 part2
 
 let doDay (n : int) =
+    let sw = Diagnostics.Stopwatch ()
+    sw.Start ()
     let result =
         match n with
         | 1 -> day1 ()
@@ -38,7 +40,7 @@ let doDay (n : int) =
         | 5 -> day5 ()
         | 6 -> day6 ()
         | _ -> raise <| NotImplementedException ()
-    printfn "Result of day %i: %s" n result
+    printfn "Result of day %i: %s (time : %i ms)" n result sw.ElapsedMilliseconds
 
 [<EntryPoint>]
 let main argv =
-- 
2.45.2