17th December solution - Advent of Code 2020 - swift

december17.swift

import Foundation

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december17.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines).filter { !$0.isEmpty }

var grid = [D4 : Bool]()
//var grid = [D3 : Bool]() // for 3D simulation

for (x,line) in lines.enumerated() {
    for (y, char) in line.enumerated() {
        grid[D4(x,y,0,0)] = char == "#"
//        grid[D3(x,y,0,0)] = char == "#" // for 3D simulation
    }
}

var newGrid = grid


for _ in 0..<6 {
    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 == 2 || activeNeighbors == 3 {
                newGrid[coordinate] = true
            } else {
                newGrid[coordinate] = false
            }
        } else {
            if activeNeighbors == 3 {
                newGrid[coordinate] = true
            } else {
                newGrid[coordinate] = false
            }
        }
    }
}
print(newGrid.filter { $0.value }.count)

struct D3 : Hashable {
    let x: Int
    let y: Int
    let z: Int
    init(_ x: Int, _ y: Int, _ z: Int) {
        self.x = x
        self.y = y
        self.z = z
    }
    
    var neighbors: [D3] {
        return [
            D3(x+1,y,z),
            D3(x+1,y,z+1),
            D3(x+1,y,z-1),
            D3(x+1,y+1,z+1),
            D3(x+1,y+1,z-1),
            D3(x+1,y+1,z),
            D3(x+1,y-1,z+1),
            D3(x+1,y-1,z-1),
            D3(x+1,y-1,z),
            D3(x,y,z+1),
            D3(x,y,z-1),
            D3(x,y+1,z+1),
            D3(x,y+1,z-1),
            D3(x,y+1,z),
            D3(x,y-1,z+1),
            D3(x,y-1,z-1),
            D3(x,y-1,z),
            D3(x-1,y,z),
            D3(x-1,y,z+1),
            D3(x-1,y,z-1),
            D3(x-1,y+1,z+1),
            D3(x-1,y+1,z-1),
            D3(x-1,y+1,z),
            D3(x-1,y-1,z+1),
            D3(x-1,y-1,z-1),
            D3(x-1,y-1,z),
        ]
    }
}

struct D4 : Hashable {
    let x: Int
    let y: Int
    let z: Int
    let w: Int
    
    init(_ x: Int, _ y: Int, _ z: Int, _ w: Int) {
        self.x = x
        self.y = y
        self.z = z
        self.w = w
    }
    init(c: D3, _ w: Int) {
        self.x = c.x
        self.y = c.y
        self.z = c.z
        self.w = w
    }
    
    var neighbors: [D4] {
        return [D4(x, y, z, w-1), D4(x, y, z, w+1)] + D3(x,y,z).neighbors.flatMap { [D4($0.x,$0.y,$0.z,w), D4($0.x,$0.y,$0.z,w+1), D4($0.x,$0.y,$0.z,w-1)] }
    }
}