aoc2021-day6-part2

gistfile1.txt

import Foundation

func loadInput() -> [Int] {
    let url = URL(fileURLWithPath: "/Volumes/Synology/Projects/Advent of Code 2021/Day 6/input-1.txt")
    var s = ""
    
    do {
        s = try String(contentsOf: url)
    }
    catch {
        print("Can't open \(url)")
        return []
    }

    let input = s.split(separator: ",")
    var allFish: [Int] = []
    
    for inputLine in input {
        allFish.append(Int(inputLine)!)
    }
    
    return allFish
}

func calcPopulationFromOneFish(startValue: Int, days: Int) -> Int
{
    var val = startValue
    var pop = 1
    var spawned = false

    for day in 1 ... days {

        spawned = false

        val -= 1

        if val == 0 {
            spawned = true
            val = 7
        }

        if spawned {
            let daysLeft = days - day
            
            if daysLeft > 0 {
                let cachedValue = cache[daysLeft]
                
                if cachedValue == -1 {
                    let spawnedFishPopulation = calcPopulationFromOneFish(startValue: 9, days: daysLeft)
                    pop += spawnedFishPopulation
                    cache[daysLeft] = spawnedFishPopulation
                }
                else {
                    pop += cachedValue
                }
            }
        }
    }

    return pop
}

func part2() {
    var total = 0
    let days = 256
    
    for startVal in allFish {
        let result = calcPopulationFromOneFish(startValue: startVal, days: days)
        total += result
    }
    
    print(total)
}

let allFish = loadInput()
print("Initial state: \(allFish)")

var cache: [Int] = Array(repeating: -1, count: 1000)

part2()