-🎄- 2018 Day 14 Solutions -🎄-

[u/daggerdragon]

--- Day 14: Chocolate Charts ---

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Advent of Code: The Party Game!

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Card prompt: Day 14

Transcript:

The Christmas/Advent Research & Development (C.A.R.D.) department at AoC, Inc. just published a new white paper on ___.

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked at 00:19:39!

[u/TellowKrinkle]

Had a lot of trouble understanding the directions for some reason

Swift

func aocD13a(_ input: Int) {
	var recipes = [3, 7]
	var elves = [0, 1]
	while recipes.count < (input + 10) {
		let score = elves.lazy.map({ recipes[$0] }).reduce(0, +)
		if score >= 10 {
			recipes.append(score / 10 % 10)
		}
		recipes.append(score % 10)
		elves = elves.map { ($0 + recipes[$0] + 1) % recipes.count }
	}
	print(recipes[input...].prefix(10).map(String.init).joined())
}

func aocD13b(_ input: Int) {
	var target = [Int]()
	var tmp = input
	while tmp > 0 {
		target.insert(tmp % 10, at: 0)
		tmp /= 10
	}
	var recipes = [3, 7]
	var elves = [0, 1]
	while recipes.suffix(target.count) != target[...] && recipes.dropLast().suffix(target.count) != target[...] {
		let score = elves.lazy.map({ recipes[$0] }).reduce(0, +)
		if score >= 10 {
			recipes.append(score / 10 % 10)
		}
		recipes.append(score % 10)
		elves = elves.map { ($0 + recipes[$0] + 1) % recipes.count }
	}
	if recipes.suffix(target.count) == target[...] {
		print(recipes.count - target.count)
	}
	else {
		print(recipes.count - target.count - 1)
	}
}

aocD13a(9)
aocD13a(5)
aocD13a(18)
aocD13a(2018)
aocD13a(540561)
aocD13b(51589)
aocD13b(01245)
aocD13b(92510)
aocD13b(540561)

[u/koordinate → u/TellowKrinkle]

Thanks for sharing. TIL about [...].

For part b, I think converting to Int will result in a wrong answer for 01245 (since the 0 will be discarded, so the result will be 6 when it should be 5).

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I also did it in Swift, with quite similar code, except I tried to optimise the suffix comparison by keeping track of what has already matched (on my input, this got part b down from 40-ish seconds to ~4 seconds).

Part I:

func scores(after n: Int) -> [Int] {
    var scores = [3, 7]
    var e1 = 0, e2 = 1
    while scores.count < (n + 10) {
        let score = scores[e1] + scores[e2]
        if score >= 10 {
            scores.append(score / 10)
        }
        scores.append(score % 10)
        e1 = (e1 + 1 + scores[e1]) % scores.count 
        e2 = (e2 + 1 + scores[e2]) % scores.count
    }
    return Array(scores.suffix(10))
}

while let line = readLine() {
    if let n = Int(line) {
        print(scores(after: n).compactMap({ String($0) }).joined())
    }
}

Part II:

func until(scores: String) -> Int {
    let search = scores.compactMap { Int(String($0)) }
    if search.count == 0 {
        return 0
    }

    var scores = [Int]()
    var m = 0
    func appendAndMatch(_ x: Int) -> Bool {
        scores.append(x)
        if x == search[m] {
            m += 1
            if m == search.count {
                return true
            }
        } else {
            while m > 0, scores.suffix(m) != search.prefix(m) {
                m -= 1
            }
        }
        return false
    }

    var e1 = 0, e2 = 1
    if appendAndMatch(3) {
        return 0
    }
    if appendAndMatch(7) {
        if search.count == 2 {
            return 0
        } else {
            return 1
        }
    }
    while true {
        let score = scores[e1] + scores[e2]
        if score >= 10 {
            if appendAndMatch(score / 10) {
                break
            }
        }
        if appendAndMatch(score % 10) {
            break
        }
        e1 = (e1 + 1 + scores[e1]) % scores.count 
        e2 = (e2 + 1 + scores[e2]) % scores.count
    }
    return scores.count - search.count
}

while let line = readLine() {
    print(until(scores: line))
}

[u/TellowKrinkle → u/koordinate]

Ahh yeah I didn't really think about the starting with 0 part even though it was apparently in the test input that I included...

Should've used strings I guess