Data commit

Task/Aliquot-sequence-classifications/Swift/aliquot-sequence-classifications.swift

@@ -0,0 +1,67 @@
+extension BinaryInteger {
+  @inlinable
+  public func factors(sorted: Bool = true) -> [Self] {
+    let maxN = Self(Double(self).squareRoot())
+    var res = Set<Self>()
+
+    for factor in stride(from: 1, through: maxN, by: 1) where self % factor == 0 {
+      res.insert(factor)
+      res.insert(self / factor)
+    }
+
+    return sorted ? res.sorted() : Array(res)
+  }
+}
+
+struct SeqClass: CustomStringConvertible {
+  var seq: [Int]
+  var desc: String
+
+  var description: String {
+    return "\(desc):    \(seq)"
+  }
+}
+
+func classifySequence(k: Int, threshold: Int = 1 << 47) -> SeqClass {
+  var last = k
+  var seq = [k]
+
+  while true {
+    last = last.factors().dropLast().reduce(0, +)
+    seq.append(last)
+
+    let n = seq.count
+
+    if last == 0 {
+      return SeqClass(seq: seq, desc: "Terminating")
+    } else if n == 2 && last == k {
+      return SeqClass(seq: seq, desc: "Perfect")
+    } else if n == 3 && last == k {
+      return SeqClass(seq: seq, desc: "Amicable")
+    } else if n >= 4 && last == k {
+      return SeqClass(seq: seq, desc: "Sociable[\(n - 1)]")
+    } else if last == seq[n - 2] {
+      return SeqClass(seq: seq, desc: "Aspiring")
+    } else if seq.dropFirst().dropLast(2).contains(last) {
+      return SeqClass(seq: seq, desc: "Cyclic[\(n - 1 - seq.firstIndex(of: last)!)]")
+    } else if n == 16 || last > threshold {
+      return SeqClass(seq: seq, desc: "Non-terminating")
+    }
+  }
+
+  fatalError()
+}
+
+for i in 1...10 {
+  print("\(i): \(classifySequence(k: i))")
+}
+
+print()
+
+for i in [11, 12, 28, 496, 220, 1184, 12496, 1264460, 790, 909, 562, 1064, 1488] {
+  print("\(i): \(classifySequence(k: i))")
+}
+
+print()
+
+print("\(15355717786080): \(classifySequence(k: 15355717786080))")