11th December solution - Advent of Code - swift

december11_1.swift

var iterations = 0
var newGrid = grid
repeat {
    grid = newGrid
    newGrid = [String]()
    for (rowIndex, row) in grid.enumerated() {
        var newRow = ""
        for (columnIndex, element) in row.enumerated() {
            if element == "L" {
                let count = countAdjacentChars(of: "#", in: grid, at: (columnIndex, rowIndex), allowedMismatches: 8)
                if count == 0 {
                    newRow += "#"
                } else {
                    newRow += "L"
                }
            } else if element == "#" {
                let count = countAdjacentChars(of: "#", in: grid, at: (columnIndex, rowIndex), allowedMismatches: 4)
                if count >= 4 {
                    newRow += "L"
                } else {
                    newRow += "#"
                }
            } else if element == "." {
                newRow += "."
            }
        }
        newGrid.append(newRow)
    }
    iterations += 1
    print(iterations)
} while grid != newGrid


print(newGrid.reduce(0, { (result, row) -> Int in
    result + row.filter { $0 == "#" }.count
}))

func countAdjacentChars(of char: Character, in localGrid:[String], at position :(Int, Int), allowedMismatches: Int) -> Int {
    let directions = [(1,1), (1,0), (0,1), (-1,1), (-1,0), (-1,-1), (0,-1), (1,-1)]
    var count = 0
    var mismatches = 0

    for direction in directions {
        let x = position.0 + direction.0
        let y = position.1 + direction.1
        if y >= 0 && y < localGrid.count && x >= 0 && x < localGrid[0].count {
            let row = Array(localGrid[y])
            let element = row[x ..< x + 1].first
            if element == char {
                count += 1
            } else {
                mismatches += 1
                if (mismatches > allowedMismatches) {
                    return count
                }
            }
        }
    }
    return count
}

december11_2.swift

var iterations = 0
var newGrid = grid
repeat {
    grid = newGrid
    newGrid = [String]()
    for (rowIndex, row) in grid.enumerated() {
        var newRow = ""
        for (columnIndex, element) in row.enumerated() {
            if element == "L" {
                let count = countAdjacentChars2(of: "#", in: grid, at: (columnIndex, rowIndex))
                if count == 0 {
                    newRow += "#"
                } else {
                    newRow += "L"
                }
            } else if element == "#" {
                let count = countAdjacentChars2(of: "#", in: grid, at: (columnIndex, rowIndex))
                if count >= 5 {
                    newRow += "L"
                } else {
                    newRow += "#"
                }
            } else if element == "." {
                newRow += "."
            }
        }
        newGrid.append(newRow)
    }
    iterations += 1
    print(iterations)
} while grid != newGrid


print(newGrid.reduce(0, { (result, row) -> Int in
    result + row.filter { $0 == "#" }.count
}))

func countAdjacentChars2(of char: Character, in localGrid:[String], at position :(Int, Int)) -> Int {
    let directions = [(1,1), (1,0), (0,1), (-1,1), (-1,0), (-1,-1), (0,-1), (1,-1)]
    var count = 0

    for direction in directions {
        var foundSeat = false
        var factor = 1
        while !foundSeat {
            let x = position.0 + direction.0 * factor
            let y = position.1 + direction.1 * factor
            if y >= 0 && y < localGrid.count && x >= 0 && x < localGrid[0].count {
                let row = Array(localGrid[y])
                let element = row[x ..< x + 1].first
                if element == char {
                    count += 1
                }
                if element != "." {
                    foundSeat = true
                }
                factor += 1
            } else {
                foundSeat = true
            }
        }
    }
    return count
}

december11_shared.swift

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december11.txt"
let contents = try! String(contentsOfFile: filename)
var grid = contents.components(separatedBy: CharacterSet.newlines).filter { !$0.isEmpty }

// fill seats
grid = grid.map { $0.replacingOccurrences(of: "L", with: "#")}