From 40053ef992f3bcb7bdb8faaf11e57151f4ac206a Mon Sep 17 00:00:00 2001
From: Max Nuding <max.nuding@icloud.com>
Date: Tue, 14 Dec 2021 20:13:34 +0100
Subject: [PATCH] Switched from string fiddling to actual character pairs

---
 Sources/14/14.swift | 42 ++++++++++++++++++++++--------------------
 1 file changed, 22 insertions(+), 20 deletions(-)

diff --git a/Sources/14/14.swift b/Sources/14/14.swift
index 9b6a502..6009355 100644
--- a/Sources/14/14.swift
+++ b/Sources/14/14.swift
@@ -8,17 +8,19 @@
 import Foundation
 import Runner
 
-struct Replacement {
-    let from: String
-    let to: String
+struct Pair: Hashable {
+    let first: String.Element
+    let second: String.Element
     
-    init(line: String) {
-        let r = line.components(separatedBy: " -> ")
-        from = r.first!
-        to = r.last!
+    init(_ str: String) {
+        first = str.first!
+        second = str.last!
     }
     
-    func replace(pair: String) -> String.Element? { pair == from ? to.first : nil }
+    init(first: String.Element, second: String.Element) {
+        self.first = first
+        self.second = second
+    }
 }
 
 class Day14: Runnable {
@@ -37,18 +39,17 @@ class Day14: Runnable {
         let replacements = parts.last!
             .components(separatedBy: .newlines)
             .map {$0.components(separatedBy: " -> ")}
-            .reduce(into: [String:String](), { p, c in
-                p[c.first!] = c.last!
+            .reduce(into: [Pair:String.Element](), {
+                $0[Pair($1.first!)] = $1.last!.first!
             })
         
-        var pairCounts = [String:Int]()
+        var pairCounts = [Pair:Int]()
         for i in startingPolymer.indices {
             let next = startingPolymer.index(i, offsetBy: 1)
             guard next != startingPolymer.endIndex else {
                 continue
             }
-            let pair = "\(startingPolymer[i])\(startingPolymer[next])"
-            pairCounts[pair, default: 0] += 1
+            pairCounts[Pair(first: startingPolymer[i], second: startingPolymer[next]), default: 0] += 1
         }
         var charCount = startingPolymer.reduce(into: [String.Element:Int](), {
             $0[$1, default: 0] += 1
@@ -56,15 +57,14 @@ class Day14: Runnable {
         
         for step in 1...40 {
             let tmpPairCounts = pairCounts
+            
             for pairCount in tmpPairCounts {
                 let pair = pairCount.key
                 let replacement = replacements[pair]!
                 pairCounts[pair]! -= pairCount.value
-                let firstCharacter = pair.first!
-                let secondCharacter = pair.last!
-                pairCounts["\(firstCharacter)\(replacement)", default: 0] += pairCount.value
-                pairCounts["\(replacement)\(secondCharacter)", default: 0] += pairCount.value
-                charCount[replacement.first!, default: 0] += pairCount.value
+                pairCounts[Pair(first: pair.first, second: replacement), default: 0] += pairCount.value
+                pairCounts[Pair(first: replacement, second: pair.second), default: 0] += pairCount.value
+                charCount[replacement, default: 0] += pairCount.value
             }
             if step == 10 {
                 printResult(charCount: charCount)
@@ -74,8 +74,10 @@ class Day14: Runnable {
     }
     
     func printResult(charCount: [String.Element:Int]) {
-        let maxC = charCount.max(by: {$0.value < $1.value })!
-        let minC = charCount.min(by: {$0.value < $1.value })!
+        // Sort instead of min/max so we need to only go through the dict once
+        let sorted = charCount.sorted(by: {$0.value > $1.value })
+        let maxC = sorted.first!
+        let minC = sorted.last!
         print(maxC.value - minC.value)
     }
 }