24th December solution - Advent of Code 2020 - swift

december24_1.swift

let occurences = coordinates.reduce(into: [:]) { counts, coordinate in counts[coordinate, default: 0] += 1 }

print(occurences.filter { $0.value % 2 == 1 }.count)

december24_2.swift

var grid = Dictionary(uniqueKeysWithValues:occurences.map { ($0.key,$0.value % 2 == 1) }.filter { $0.1 })

var newGrid = grid

for _ in 0..<100 {
    grid = newGrid
    for element in grid {
        let coordinate = element.key
        for neighbor in coordinate.neighbors {
            if grid[neighbor] == nil {
                grid[neighbor] = false
            }
        }
    }
    for element in grid {
        let coordinate = element.key
        var activeNeighbors = 0
        for neighbor in coordinate.neighbors {
            if grid[neighbor] == true {
                activeNeighbors += 1
            } else {
                if newGrid[neighbor] == nil {
                    newGrid[neighbor] = false
                }
            }
        }
        if grid[coordinate] == true {
            if activeNeighbors == 0 || activeNeighbors > 2 {
                newGrid[coordinate] = false
            } else {
                newGrid[coordinate] = true
            }
        } else {
            if activeNeighbors == 2 {
                newGrid[coordinate] = true
            } else {
                newGrid[coordinate] = false
            }
        }
    }
}
print(newGrid.filter { $0.value }.count)

december24_shared.swift

import Foundation


let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december24.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines).filter { !$0.isEmpty}

struct Coordinate: Hashable {
    let x: Int
    let y: Int
    
    init(_ x: Int, _ y: Int) {
        self.x = x
        self.y = y
    }
    
    var neighbors: [Coordinate] {
        return [Coordinate(x - 2, y), Coordinate(x + 2, y), Coordinate(x + 1, y + 1), Coordinate(x - 1, y + 1), Coordinate(x + 1, y - 1), Coordinate(x - 1, y - 1)]
        }
}
let diagonalDirections = [
    "se": Coordinate(1,1),
    "sw": Coordinate(-1,1),
    "nw": Coordinate(-1,-1),
    "ne": Coordinate(1,-1),
]
let lateralDirections = [
    "e": Coordinate(2,0),
    "w": Coordinate(-2,0)
]
let coordinates = lines.map { pLine -> Coordinate in
    var relativeCoordinate = Coordinate(0,0)
    var line = pLine
    var substring = ""
    while line.count > 0 || substring.count > 0 {
        while line.count > 0 && substring.count < 2 {
            substring.append(line.removeFirst())
        }
        var direction = diagonalDirections[substring]
        if direction == nil {
            direction = lateralDirections[String(substring.first!)]
            substring.removeFirst()
        } else {
            substring.removeFirst()
            substring.removeFirst()
        }
        relativeCoordinate = Coordinate(relativeCoordinate.x + direction!.x, relativeCoordinate.y + direction!.y)
    }
    return relativeCoordinate
}