[Swift 4] Update Kth Largest Element

Kth Largest Element/kthLargest.playground/Contents.swift

@@ -1,14 +1,9 @@
 //: Playground - noun: a place where people can play
 
-func kthLargest(_ a: [Int], _ k: Int) -> Int? {
-  let len = a.count
-  if k > 0 && k <= len {
-    let sorted = a.sorted()
-    return sorted[len - k]
-  } else {
-    return nil
-  }
-}
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
 
 let a = [5, 1, 3, 2, 7, 6, 4]
 
@@ -22,65 +17,6 @@ kthLargest(a, 6)
 kthLargest(a, 7)
 kthLargest(a, 8)
 
-import Foundation
-
-/* Returns a random integer in the range min...max, inclusive. */
-public func random( min: Int, max: Int) -> Int {
-  assert(min < max)
-  return min + Int(arc4random_uniform(UInt32(max - min + 1)))
-}
-
-/*
-  Swift's swap() doesn't like it if the items you're trying to swap refer to
-  the same memory location. This little wrapper simply ignores such swaps.
-*/
-public func swap<T>(_ a:inout [T], _ i: Int, _ j: Int) {
-  if i != j {
-    swap(&a[i], &a[j])
-  }
-}
-
-public func randomizedSelect<T: Comparable>(_ array: [T], order k: Int) -> T {
-  var a = array
-
-  func randomPivot<T: Comparable>(_ a: inout[T], _ low: Int, _ high: Int) -> T {
-    let pivotIndex = random(min: low, max: high)
-    swap(&a, pivotIndex, high)
-    return a[high]
-  }
-
-  func randomizedPartition<T: Comparable>(_ a: inout[T], _ low: Int, _ high: Int) -> Int {
-    let pivot = randomPivot(&a, low, high)
-    var i = low
-    for j in low..<high {
-      if a[j] <= pivot {
-        swap(&a, i, j)
-        i += 1
-      }
-    }
-    swap(&a, i, high)
-    return i
-  }
-
-  func randomizedSelect<T: Comparable>(_ a: inout [T], _ low: Int, _ high: Int, _ k: Int) -> T {
-    if low < high {
-      let p = randomizedPartition(&a, low, high)
-      if k == p {
-        return a[p]
-      } else if k < p {
-        return randomizedSelect(&a, low, p - 1, k)
-      } else {
-        return randomizedSelect(&a, p + 1, high, k)
-      }
-    } else {
-      return a[low]
-    }
-  }
-
-  precondition(a.count > 0)
-  return randomizedSelect(&a, 0, a.count - 1, k)
-}
-
 randomizedSelect(a, order: 0)
 randomizedSelect(a, order: 1)
 randomizedSelect(a, order: 2)

Kth Largest Element/kthLargest.swift → Kth Largest Element/kthLargest.playground/Sources/kthLargest.swift

@@ -4,10 +4,10 @@ import Foundation
   Returns the k-th largest value inside of an array a.
   This is an O(n log n) solution since we sort the array.
 */
-func kthLargest(a: [Int], k: Int) -> Int? {
+public func kthLargest(_ a: [Int], _ k: Int) -> Int? {
   let len = a.count
   if k > 0 && k <= len {
-    let sorted = a.sort()
+    let sorted = a.sorted()
     return sorted[len - k]
   } else {
     return nil
@@ -17,21 +17,11 @@ func kthLargest(a: [Int], k: Int) -> Int? {
 // MARK: - Randomized selection
 
 /* Returns a random integer in the range min...max, inclusive. */
-public func random(min min: Int, max: Int) -> Int {
+public func random(min: Int, max: Int) -> Int {
   assert(min < max)
   return min + Int(arc4random_uniform(UInt32(max - min + 1)))
 }
 
-/*
-  Swift's swap() doesn't like it if the items you're trying to swap refer to
-  the same memory location. This little wrapper simply ignores such swaps.
-*/
-public func swap<T>(inout a: [T], _ i: Int, _ j: Int) {
-  if i != j {
-    swap(&a[i], &a[j])
-  }
-}
-
 /*
   Returns the i-th smallest element from the array.
 
@@ -45,29 +35,29 @@ public func swap<T>(inout a: [T], _ i: Int, _ j: Int) {
 
   Expected running time: O(n) if the elements are distinct.
 */
-public func randomizedSelect<T: Comparable>(array: [T], order k: Int) -> T {
+public func randomizedSelect<T: Comparable>(_ array: [T], order k: Int) -> T {
   var a = array
 
-  func randomPivot<T: Comparable>(inout a: [T], _ low: Int, _ high: Int) -> T {
+  func randomPivot<T: Comparable>(_ a: inout [T], _ low: Int, _ high: Int) -> T {
     let pivotIndex = random(min: low, max: high)
-    swap(&a, pivotIndex, high)
+    a.swapAt(pivotIndex, high)
     return a[high]
   }
 
-  func randomizedPartition<T: Comparable>(inout a: [T], _ low: Int, _ high: Int) -> Int {
+  func randomizedPartition<T: Comparable>(_ a: inout [T], _ low: Int, _ high: Int) -> Int {
     let pivot = randomPivot(&a, low, high)
     var i = low
     for j in low..<high {
       if a[j] <= pivot {
-        swap(&a, i, j)
+        a.swapAt(i, j)
         i += 1
       }
     }
-    swap(&a, i, high)
+    a.swapAt(i, high)
     return i
   }
 
-  func randomizedSelect<T: Comparable>(inout a: [T], _ low: Int, _ high: Int, _ k: Int) -> T {
+  func randomizedSelect<T: Comparable>(_ a: inout [T], _ low: Int, _ high: Int, _ k: Int) -> T {
     if low < high {
       let p = randomizedPartition(&a, low, high)
       if k == p {