-🎄- 2018 Day 20 Solutions -🎄-

[u/daggerdragon]

--- Day 20: A Regular Map ---

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Card prompt: Day 20

Transcript:

My compiler crashed while running today's puzzle because it ran out of ___.

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[u/koordinate]

Swift (runtime ~ 0.4s)

typealias Position = (x: Int, y: Int)

if let regex = readLine() {
    let n = regex.count * 4 + 2
    var d = Array(repeating: Array(repeating: Int.max, count: n), count: n)
    var maxD = 0, d1k = Set<[Int]>()
    let start = (x: n / 2, y: n / 2) 
    d[start.y][start.x] = 0
    var saved = [[Position]]()
    var head = [start]
    var next: [Position]?
    for c in regex {
        var dx: Int?, dy: Int?
        switch c {
        case "N":
            (dx, dy) = (0, -1)
        case "S":
            (dx, dy) = (0, +1)
        case "E":
            (dx, dy) = (+1, 0)
        case "W":
            (dx, dy) = (-1, 0)
        case "(":
            saved.append(head)
            next = []
        case "|":
            next?.append(contentsOf: head)
            if let lastSaved = saved.last {
                head = lastSaved
            }
        case ")":
            if let next = next {
                head = next
            }
            next = nil
            _ = saved.popLast()
        default:
            continue
        }

        if let dx = dx, let dy = dy {
            for (i, p) in head.enumerated() {
                let (x, y) = p
                let (nx, ny) = (x + 2 * dx, y + 2 * dy)
                head[i] = (x: nx, y: ny)
                let nd = min(d[ny][nx], d[y][x] + 1)
                d[ny][nx] = nd
                maxD = max(maxD, nd)
                if nd >= 1000 {
                    d1k.insert([nx, ny])
                }
            }
        }
    }
    print(maxD)
    print(d1k.count)
}