added playground files

Author: kelvinlauKL

Mergesort/Mergesort.playground/Contents.swift

@@ -0,0 +1,52 @@
+let array = [2, 1, 5, 4, 9]
+
+func mergeSort(array: [Int]) -> [Int] {
+  guard array.count > 1 else { return array } // 1
+  let middleIndex = array.count / 2 // 2
+
+  let leftArray = mergeSort(Array(array[0..<middleIndex])) // 3
+
+  let rightArray = mergeSort(Array(array[middleIndex..<array.count])) // 4
+
+  return merge(leftPile: leftArray, rightPile: rightArray) // 5
+}
+
+func merge(leftPile leftPile: [Int], rightPile: [Int]) -> [Int] {
+  // 1
+  var leftIndex = 0
+  var rightIndex = 0
+
+  // 2
+  var orderedPile = [Int]()
+
+  // 3
+  while leftIndex < leftPile.count && rightIndex < rightPile.count {
+    if leftPile[leftIndex] < rightPile[rightIndex] {
+      orderedPile.append(leftPile[leftIndex])
+      leftIndex += 1
+    } else if leftPile[leftIndex] > rightPile[rightIndex] {
+      orderedPile.append(rightPile[rightIndex])
+      rightIndex += 1
+    } else {
+      orderedPile.append(leftPile[leftIndex])
+      leftIndex += 1
+      orderedPile.append(rightPile[rightIndex])
+      rightIndex += 1
+    }
+  }
+
+  // 4
+  while leftIndex < leftPile.count {
+    orderedPile.append(leftPile[leftIndex])
+    leftIndex += 1
+  }
+
+  while rightIndex < rightPile.count {
+    orderedPile.append(rightPile[rightIndex])
+    rightIndex += 1
+  }
+
+  return orderedPile
+}
+
+let sortedArray = mergeSort(array)

Mergesort/Mergesort.playground/contents.xcplayground

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+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<playground version='5.0' target-platform='ios'>
+    <timeline fileName='timeline.xctimeline'/>
+</playground>

Mergesort/Mergesort.playground/timeline.xctimeline

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+<?xml version="1.0" encoding="UTF-8"?>
+<Timeline
+   version = "3.0">
+   <TimelineItems>
+   </TimelineItems>
+</Timeline>