Data commit

Task/Taxicab-numbers/Swift/taxicab-numbers.swift

@@ -0,0 +1,48 @@
+extension Array {
+  func combinations(_ k: Int) -> [[Element]] {
+    return Self._combinations(slice: self[startIndex...], k)
+  }
+
+  static func _combinations(slice: Self.SubSequence, _ k: Int) -> [[Element]] {
+    guard k != 1 else {
+      return slice.map({ [$0] })
+    }
+
+    guard k != slice.count else {
+      return [slice.map({ $0 })]
+    }
+
+    let chopped = slice[slice.index(after: slice.startIndex)...]
+
+    var res = _combinations(slice: chopped, k - 1).map({ [[slice.first!], $0].flatMap({ $0 }) })
+
+    res += _combinations(slice: chopped, k)
+
+    return res
+  }
+}
+
+let cubes = (1...).lazy.map({ $0 * $0 * $0 })
+let taxis =
+  Array(cubes.prefix(1201))
+    .combinations(2)
+    .reduce(into: [Int: [[Int]]](), { $0[$1[0] + $1[1], default: []].append($1) })
+
+
+let res =
+  taxis
+    .lazy
+    .filter({ $0.value.count > 1 })
+    .sorted(by: { $0.key < $1.key })
+    .map({ ($0.key, $0.value) })
+    .prefix(2006)
+
+print("First 25 taxicab numbers:")
+for taxi in res[..<25] {
+  print(taxi)
+}
+
+print("\n2000th through 2006th taxicab numbers:")
+for taxi in res[1999..<2006] {
+  print(taxi)
+}