Data commit

Task/Padovan-sequence/Swift/padovan-sequence.swift

@@ -0,0 +1,65 @@
+import Foundation
+
+class PadovanRecurrence: Sequence, IteratorProtocol {
+    private var p = [1, 1, 1]
+    private var n = 0
+
+    func next() -> Int? {
+        let pn = n < 3 ? p[n] : p[0] + p[1]
+        p[0] = p[1]
+        p[1] = p[2]
+        p[2] = pn
+        n += 1
+        return pn
+    }
+}
+
+class PadovanFloor: Sequence, IteratorProtocol {
+    private let P = 1.324717957244746025960908854
+    private let S = 1.0453567932525329623
+    private var n = 0
+
+    func next() -> Int? {
+        let p = Int(floor(pow(P, Double(n - 1)) / S + 0.5))
+        n += 1
+        return p
+    }
+}
+
+class PadovanLSystem: Sequence, IteratorProtocol {
+    private var str = "A"
+
+    func next() -> String? {
+        let result = str
+        var next = ""
+        for ch in str {
+            switch (ch) {
+            case "A": next.append("B")
+            case "B": next.append("C")
+            default: next.append("AB")
+            }
+        }
+        str = next
+        return result
+    }
+}
+
+print("First 20 terms of the Padovan sequence:")
+for p in PadovanRecurrence().prefix(20) {
+    print("\(p)", terminator: " ")
+}
+print()
+
+var b = PadovanRecurrence().prefix(64)
+    .elementsEqual(PadovanFloor().prefix(64))
+print("\nRecurrence and floor functions agree for first 64 terms? \(b)")
+
+print("\nFirst 10 strings produced from the L-system:");
+for p in PadovanLSystem().prefix(10) {
+    print(p, terminator: " ")
+}
+print()
+
+b = PadovanLSystem().prefix(32).map{$0.count}
+    .elementsEqual(PadovanRecurrence().prefix(32))
+print("\nLength of first 32 strings produced from the L-system = Padovan sequence? \(b)")