20th December solution - Advent Of Code 2020 - swift

december20_1.swift

import Foundation

struct Tile {
    let id: Int
    let imageData: [String]
    var borders: [String] {
        var list = [String]()
        list.append(imageData.first!)
        list.append(String(imageData.last!))
        list.append(String(imageData.map { $0.first! }))
        list.append(String(imageData.map { $0.last! }))
        return list
    }
    var flippedVert: Tile {
        return Tile(id: self.id, imageData: imageData.reversed() as [String])
    }
    var flippedHorz: Tile {
        return Tile(id: self.id, imageData: imageData.map { String($0.reversed()) })
    }
    
    var allPossibleBorders: [String] {
            var list = [String]()
        list.append(contentsOf: borders)
        list.append(contentsOf: borders.map{String($0.reversed())})
        return list
        }
}

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december20.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines).filter { !$0.isEmpty}

var tiles = [Tile]()
var currentTileId = -1
var currentImageData = [String]()
for line in lines {
    if line.contains("Tile") {
        if currentTileId != -1 {
            tiles.append(Tile(id: currentTileId, imageData: currentImageData))
        }
        currentTileId = Int(line.components(separatedBy: "Tile ")[1].dropLast())!
        currentImageData = [String]()
    } else {
        currentImageData.append(line)
    }
}
tiles.append(Tile(id: currentTileId, imageData: currentImageData))


print(tiles.count)
var cornerTiles = [Tile]()
var i = 0
while i < tiles.count {
    let tile = tiles[i]
    if countBordersMatched(tile) == 2 {
        cornerTiles.append(tile)
    }
    i += 1
}
print(cornerTiles.count)
print(cornerTiles.map { $0.id }.reduce(1, *))


func countBordersMatched(_ tile: Tile) -> Int {
    var matchingBorders = 0
    borders: for border in tile.borders {
        for j in 0..<tiles.count {
            let cTile = tiles[j]
            if cTile.id != tile.id {
                if cTile.allPossibleBorders.contains(border) {
                    matchingBorders += 1
                    continue borders
                }
            }
        }
    }
    return matchingBorders
}