14b

Sources/14/14.swift

@@ -33,42 +33,49 @@ class Day14: Runnable {
         let parts = input
             .trimmingCharacters(in: .newlines)
             .components(separatedBy: "\n\n")
-        var startingPolymer = parts.first!
+        let startingPolymer = parts.first!
         let replacements = parts.last!
             .components(separatedBy: .newlines)
-            .map(Replacement.init)
+            .map {$0.components(separatedBy: " -> ")}
+            .reduce(into: [String:String](), { p, c in
+                p[c.first!] = c.last!
+            })
         
-        for step in 1...10 {
-            var inserts = [(String.Index, Character)]()
+        var pairCounts = [String:Int]()
         for i in startingPolymer.indices {
             let next = startingPolymer.index(i, offsetBy: 1)
             guard next != startingPolymer.endIndex else {
                 continue
             }
-                var pair = startingPolymer[i]/* + startingPolymer[next]*/
-                let p = "\(startingPolymer[i])\(startingPolymer[next])"
-                for replacement in replacements {
-                    if let c = replacement.replace(pair: p) {
-                        inserts.append((next, c))
-                        break
+            let pair = "\(startingPolymer[i])\(startingPolymer[next])"
+            pairCounts[pair, default: 0] += 1
         }
-                }
-            }
-            
-            var tmp = startingPolymer
-            var count = 0
-            for r in inserts {
-                let idx = tmp.index(r.0, offsetBy: count)
-                tmp.insert(r.1, at: idx)
-                count += 1
-            }
-            startingPolymer = tmp
-        }
-        let charCounts = startingPolymer.reduce(into: [String.Element: Int](), {
+        var charCount = startingPolymer.reduce(into: [String.Element:Int](), {
             $0[$1, default: 0] += 1
         })
-        let maxC = charCounts.max(by: {$0.value < $1.value })!
-        let minC = charCounts.min(by: {$0.value < $1.value })!
+        
+        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
+            }
+            if step == 10 {
+                printResult(charCount: charCount)
+            }
+        }
+        printResult(charCount: charCount)
+    }
+    
+    func printResult(charCount: [String.Element:Int]) {
+        let maxC = charCount.max(by: {$0.value < $1.value })!
+        let minC = charCount.min(by: {$0.value < $1.value })!
         print(maxC.value - minC.value)
     }
 }