Data commit

Task/Binary-search/Swift/binary-search-1.swift

@@ -0,0 +1,10 @@
+func binarySearch<T: Comparable>(xs: [T], x: T) -> Int? {
+  var recurse: ((Int, Int) -> Int?)!
+  recurse = {(low, high) in switch (low + high) / 2 {
+    case _ where high < low: return nil
+    case let mid where xs[mid] > x: return recurse(low, mid - 1)
+    case let mid where xs[mid] < x: return recurse(mid + 1, high)
+    case let mid: return mid
+  }}
+  return recurse(0, xs.count - 1)
+}

Task/Binary-search/Swift/binary-search-2.swift

@@ -0,0 +1,11 @@
+func binarySearch<T: Comparable>(xs: [T], x: T) -> Int? {
+  var (low, high) = (0, xs.count - 1)
+  while low <= high {
+    switch (low + high) / 2 {
+      case let mid where xs[mid] > x: high = mid - 1
+      case let mid where xs[mid] < x: low = mid + 1
+      case let mid: return mid
+    }
+  }
+  return nil
+}

Task/Binary-search/Swift/binary-search-3.swift

@@ -0,0 +1,15 @@
+func testBinarySearch(n: Int) {
+  let odds = Array(stride(from: 1, through: n, by: 2))
+  let result = flatMap(0...n) {binarySearch(odds, $0)}
+  assert(result == Array(0..<odds.count))
+  println("\(odds) are odd natural numbers")
+  for it in result {
+    println("\(it) is ordinal of \(odds[it])")
+  }
+}
+
+testBinarySearch(12)
+
+func flatMap<T, U>(source: [T], transform: (T) -> U?) -> [U] {
+  return source.reduce([]) {(var xs, x) in if let x = transform(x) {xs.append(x)}; return xs}
+}