aoc2021/Sources/06/06.swift

//
//  File.swift
//
//
//  Created by Max Nuding on 05.12.21.
//

import Foundation
import Runner

struct Day06: Runnable {
    let inputPath: String
    
    func run() {
        let input = try! String(contentsOfFile: inputPath)
        let internalCounters = input
            .trimmingCharacters(in: .newlines)
            .components(separatedBy: ",")
            .map { Int($0)! }
        run(fish: internalCounters, numDays: 80)
        run(fish: internalCounters, numDays: 256)
    }
    
    func run(fish: [Int], numDays: Int) {
        var fishCount = Dictionary(grouping: fish, by: { $0 }).mapValues { $0.count }
        
        for _ in 1...numDays {
            var tmpFishCount = fishCount
                .filter { $0.key >= 0 }
                .reduce(into: [:]) { $0[$1.key-1, default: 0] = $1.value }
            let countPregnant = tmpFishCount[-1] ?? 0
            tmpFishCount[8] = countPregnant
            tmpFishCount[6] = (tmpFishCount[6] ?? 0) + countPregnant
            tmpFishCount[-1] = 0
            
            fishCount = tmpFishCount
        }
        print(fishCount.values.reduce(0, +))
    }
}