Add 2017 solutions

2017/Advent1.playground/Pages/Day 3 - 1 Spiral.xcplaygroundpage/Contents.swift

@@ -0,0 +1,23 @@
+//: [Previous](@previous)
+
+import Foundation
+
+func shell(_ value: Int) -> Int {
+    return Int(ceil((sqrt(Double(value)) - 1) / 2))
+}
+
+func biggestValue(_ shell: Int) -> Int {
+    return (2 * shell + 1) * (2 * shell + 1)
+}
+
+let value = 16
+
+let s = shell(value)
+
+let shellStart = biggestValue(s - 1) + 1
+
+let shellPosition = value - shellStart
+
+(Float(shellPosition) / 2 + 1) / 2
+
+//: [Next](@next)