3rd December solution - Advent of Code 2020 - swift

december03_1.swift

let treeCount = countTrees(in: lines, dX: 3, dY: 1)
print(treeCount)

december03_2.swift

  var treeCounts = [Int]()
  treeCounts.append(countTrees(in: lines, dX: 1, dY: 1))
  treeCounts.append(countTrees(in: lines, dX: 3, dY: 1))
  treeCounts.append(countTrees(in: lines, dX: 5, dY: 1))
  treeCounts.append(countTrees(in: lines, dX: 7, dY: 1))
  treeCounts.append(countTrees(in: lines, dX: 1, dY: 2))
  print(treeCounts.reduce(1, *))

december03_shared.swift

func countTrees(in lines: [String.SubSequence], dX: Int, dY: Int) -> Int {
    var x = 0
    var treeCount = 0
    for lineIndex in stride(from: 0, to: lines.count - 1, by: dY) {
        let line = String(lines[lineIndex])
        if line.charAt(x % line.count) == "#"
        {
            treeCount += 1
        }
        x += dX
    }
    return treeCount
}

extension String {
    func charAt(_ i: Int) -> Character {
        return Array(self)[i]
    }
}

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december03.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.split(separator:"\n")