Update README.markdown for some places and Selection Sampling Content.swift improvement

Count Occurrences/README.markdown

@@ -28,7 +28,7 @@ func countOccurrences<T: Comparable>(of key: T, in array: [T]) -> Int {
  var high = array.count
  while low < high {
  let midIndex = low + (high - low)/2
- if a[midIndex] < key {
+ if array[midIndex] < key {
  low = midIndex + 1
  } else {
  high = midIndex
@@ -42,7 +42,7 @@ func countOccurrences<T: Comparable>(of key: T, in array: [T]) -> Int {
  var high = array.count
  while low < high {
  let midIndex = low + (high - low)/2
- if a[midIndex] > key {
+ if array[midIndex] > key {
  high = midIndex
  } else {
  low = midIndex + 1

Kth Largest Element/README.markdown

@@ -88,7 +88,7 @@ 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)
+ let pivotIndex = Int.random(in: low...high)
  a.swapAt(pivotIndex, high)
  return a[high]
  }

Selection Sampling/README.markdown

@@ -7,6 +7,12 @@ Let's say you have a deck of 52 playing cards and you need to draw 10 cards at r
 Here's a very fast version:
 
 ```swift
+public func random(min: Int, max: Int) -> Int {
+ assert(min < max)
+ return min + Int(arc4random_uniform(UInt32(max - min + 1)))
+}
+
+
 func select<T>(from a: [T], count k: Int) -> [T] {
  var a = a
  for i in 0..<k {

Selection Sampling/SelectionSampling.playground/Contents.swift

@@ -19,7 +19,7 @@ func select<T>(from a: [T], count k: Int) -> [T] {
  for i in 0..<k {
  let r = random(min: i, max: a.count - 1)
  if i != r {
- swap(&a[i], &a[r])
+  a.swapAt(i, r)
  }
  }
  return Array(a[0..<k])