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2020/day3/main.swift

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+let input = loadData(day: 3).lines()
+
+/// - returns true if a tree is at that position, false if it is empty
+func get(x: Int, y: Int) -> Bool {
+    let line = input[y]
+    let index = line.index(line.startIndex, offsetBy: x % line.count)
+    return line[index] == "#"
+}
+
+func calculate(dx: Int, dy: Int) -> Int {
+var x = 0
+var y = 0
+
+var trees = 0
+
+while y < input.count {
+    if get(x: x, y: y) {
+        trees += 1
+    }
+
+    x += dx
+    y += dy
+}
+
+    return trees
+}
+
+let trees = calculate(dx: 3, dy: 1)
+print("trees", trees)
+
+
+print("combined", calculate(dx: 1, dy: 1) * calculate(dx: 3, dy: 1) * calculate(dx: 5, dy: 1) * calculate(dx: 7, dy: 1) * calculate(dx: 1, dy: 2))