07b

Sources/07/07.swift

@@ -17,13 +17,32 @@ struct Day07: Runnable {
             .trimmingCharacters(in: .newlines)
             .components(separatedBy: ",")
             .map { Int($0)! }
-        run(horizontalPositions: horizontalPositions)
+        runA(horizontalPositions: horizontalPositions)
+        runB(horizontalPositions: horizontalPositions)
     }
     
-    func run(horizontalPositions: [Int]) {
+    func runA(horizontalPositions: [Int]) {
         let median = horizontalPositions.sorted()[horizontalPositions.count / 2]
         let distancesToMedian = horizontalPositions.map { abs(median - $0) }
         let toalFuel = distancesToMedian.reduce(0,+)
         print(toalFuel)
     }
+    
+    func runB(horizontalPositions: [Int]) {
+        let average = Double(horizontalPositions.reduce(0, +)) / Double(horizontalPositions.count)
+        let roundedDown = Int(floor(average))
+        let roundedUp = Int(ceil(average))
+        let fuelForRoundedDown = fuelConsumptionFor(horizontalPositions: horizontalPositions, toPosition: roundedDown)
+        let fuelForRoundedUp = fuelConsumptionFor(horizontalPositions: horizontalPositions, toPosition: roundedUp)
+        print(min(fuelForRoundedDown, fuelForRoundedUp))
+    }
+    
+    func fuelConsumptionFor(horizontalPositions: [Int], toPosition targetPos: Int) -> Int {
+        horizontalPositions.map { fuelConsumptionFor(numSteps: abs(targetPos - $0)) }.reduce(0,+)
+    }
+    
+    func fuelConsumptionFor(numSteps: Int) -> Int {
+        let dv = Double(numSteps)
+        return Int((pow(dv, 2) + dv) / 2.0)
+    }
 }

Sources/07/main.swift

@@ -8,4 +8,5 @@
 import Foundation
 import Runner
 
+Runner(target: Day07.self, day: "07", isTest: true).run()
 Runner(target: Day07.self, day: "07", isTest: false).run()