From 3642e40915efe51c561e87f5109c5cc725c716ab Mon Sep 17 00:00:00 2001
From: Ummon <greg.burri@gmail.com>
Date: Thu, 21 Dec 2017 10:29:59 +0100
Subject: [PATCH] Fix part 1, replace euclidean norm by manhattan norm.

---
 AdventOfCode2017/AdventOfCode2017.fsproj | 2 +-
 AdventOfCode2017/Day20.fs                | 7 +++----
 AdventOfCode2017/Program.fs              | 1 -
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/AdventOfCode2017/AdventOfCode2017.fsproj b/AdventOfCode2017/AdventOfCode2017.fsproj
index 0229b06..4cc42dc 100644
--- a/AdventOfCode2017/AdventOfCode2017.fsproj
+++ b/AdventOfCode2017/AdventOfCode2017.fsproj
@@ -37,7 +37,7 @@
     <PlatformTarget>AnyCPU</PlatformTarget>
     <DocumentationFile>bin\$(Configuration)\$(AssemblyName).XML</DocumentationFile>
     <Prefer32Bit>true</Prefer32Bit>
-    <StartArguments>19</StartArguments>
+    <StartArguments>20</StartArguments>
   </PropertyGroup>
   <PropertyGroup>
     <MinimumVisualStudioVersion Condition="'$(MinimumVisualStudioVersion)' == ''">11</MinimumVisualStudioVersion>
diff --git a/AdventOfCode2017/Day20.fs b/AdventOfCode2017/Day20.fs
index 3ab08b0..031fadd 100644
--- a/AdventOfCode2017/Day20.fs
+++ b/AdventOfCode2017/Day20.fs
@@ -5,7 +5,7 @@ open System
 type Vec =
     { X : float; Y : float; Z : float }
     with
-        member this.SquareNorm = this.X ** 2. + this.Y ** 2. + this.Z ** 2.
+        member this.ManhattanNorm = abs this.X  + abs this.Y + abs this.Z
 
 type Particule =
     { Pos : Vec; V : Vec; A : Vec }
@@ -22,9 +22,8 @@ let parseInput (input : string[]) : Particule[] =
             }
     )
 
-// This is wrong with a manhattan distance :( but works in my case :)
 let nearestZero (particules : Particule[]) : int =
-    particules |> Array.indexed |> Array.minBy (fun (_, p) -> p.A.SquareNorm, p.V.SquareNorm, p.Pos.SquareNorm) |> fst
+    particules |> Array.indexed |> Array.minBy (fun (_, p) -> p.A.ManhattanNorm, p.V.ManhattanNorm, p.Pos.ManhattanNorm) |> fst
 
 let collide (p1 : Particule) (p2 : Particule) : int option =
     // https://www.wolframalpha.com/input/?i=solve+a%2B(b%2Bc%2F2)*t%2B1%2F2*c*t%5E2+-+d-(e%2Bf%2F2)*t-1%2F2*f*t%5E2+%3D+0
@@ -52,7 +51,7 @@ let collide (p1 : Particule) (p2 : Particule) : int option =
     let tsInt =
         ts |> List.choose (
             fun t ->
-                let tRound = Math.Round (t, 5) * 10000. |> int
+                let tRound = Math.Round (t, 4) * 10000. |> int
                 if tRound % 10000 = 0 then Some tRound else None
         )
 
diff --git a/AdventOfCode2017/Program.fs b/AdventOfCode2017/Program.fs
index 170adb9..adf50dd 100644
--- a/AdventOfCode2017/Program.fs
+++ b/AdventOfCode2017/Program.fs
@@ -89,7 +89,6 @@ let day19 () =
     sprintf "part1 = %A, part2 = %A" word length
 
 let day20 () =
-    //let input = File.ReadAllLines "../../Data/day20_ben.input" |> Day20.parseInput
     let input = File.ReadAllLines "Data/day20.input" |> Day20.parseInput
     sprintf "part1 = %A, part2 = %A" (Day20.nearestZero input) (Day20.nbAlive input)
 
-- 
2.45.2