AOC 2022 day 23

main.swift

// https://adventofcode.com/2022/day/23

import AOC
import Preamble

let input = readInput()
let xinput = """
....#..
..###.#
#...#.#
.#...##
#.###..
##.#.##
.#..#..
"""

var elves = Grid(asciiArt: input).reduce(into: Set<Point>()) {
    if $2 == "#" { $0.insert($1) }
}

var dirses: [[Vector]] = [
    [.NE, .N, .NW],
    [.SE, .S, .SW],
    [.NW, .W, .SW],
    [.NE, .E, .SE],
]

func step() -> Bool {
    var props: [Point: [Point]] = [:]
    for e in elves {
        guard Vector.all8.contains(where: { elves.contains(e + $0) }) else { continue }
        for dirs in dirses {
            if dirs.allSatisfy({ !elves.contains(e + $0) }) {
                let t = e + dirs[1]
                props[t, default: []].append(e)
                break
            }
        }
    }

    var moved = false
    for (t, fs) in props where fs.count == 1 {
        elves.remove(fs[0])
        elves.insert(t)
        moved = true
    }

    let d = dirses.removeFirst()
    dirses.append(d)

    return moved
}

var r = 1

while true {
    guard step() else { break }
    if r == 10 {
        let box = elves.boundingBox()!
        let p1 = box.sequence.lazy.filter { !elves.contains($0) }.makeArray().count
        p1 |> printAndCopy
        // 2605 WRONG didn't break after adding a proposal; didn't check elf has a neighbor before allowing a proposal
        // 4000
    }
    r += 1
}

r |> printAndCopy
// 1039 WRONG off-by-one
// 1040