Initial data commit

Task/Sorting-algorithms-Merge-sort/Swift/sorting-algorithms-merge-sort.swift

@@ -0,0 +1,52 @@
+// Merge Sort in Swift 4.2
+// Source: https://github.com/raywenderlich/swift-algorithm-club/tree/master/Merge%20Sort
+// NOTE: by use of generics you can make it sort arrays of any type that conforms to
+//       Comparable protocol, however this is not always optimal
+
+import Foundation
+
+func mergeSort(_ array: [Int]) -> [Int] {
+  guard array.count > 1 else { return array }
+
+  let middleIndex = array.count / 2
+
+  let leftPart = mergeSort(Array(array[0..<middleIndex]))
+  let rightPart = mergeSort(Array(array[middleIndex..<array.count]))
+
+  func merge(left: [Int], right: [Int]) -> [Int] {
+    var leftIndex = 0
+    var rightIndex = 0
+
+    var merged = [Int]()
+    merged.reserveCapacity(left.count + right.count)
+
+    while leftIndex < left.count && rightIndex < right.count {
+      if left[leftIndex] < right[rightIndex] {
+        merged.append(left[leftIndex])
+        leftIndex += 1
+      } else if left[leftIndex] > right[rightIndex] {
+        merged.append(right[rightIndex])
+        rightIndex += 1
+      } else {
+        merged.append(left[leftIndex])
+        leftIndex += 1
+        merged.append(right[rightIndex])
+        rightIndex += 1
+      }
+    }
+
+    while leftIndex < left.count {
+      merged.append(left[leftIndex])
+      leftIndex += 1
+    }
+
+    while rightIndex < right.count {
+      merged.append(right[rightIndex])
+      rightIndex += 1
+    }
+
+    return merged
+  }
+
+  return merge(left: leftPart, right: rightPart)
+}