Merge pull request deutranium#229 from Heniboj/master

merge sort in Swift

Author: codelixir

Diff for: sortingAlgo/mergeSort/mergeSort.swift

@@ -0,0 +1,47 @@
+// a function that merges two arrys
+func merge(_ array_1: inout [Int], _ low: Int, _ mid: Int, _ high: Int) {
+    var i = low
+    var j = mid + 1
+    var k = 0
+    
+    var array_2: [Int] = [Int](repeating: 0, count: high - low + 1)
+    
+    while i <= mid && j <= high {
+        if array_1[i] <= array_1[j] {
+            array_2[k] = array_1[i]
+            k += 1
+            i += 1
+        }
+        else {
+            array_2[k] = array_1[j]
+            k += 1
+            j += 1
+        }
+    }
+    
+    while i <= mid {
+        array_2[k] = array_1[i]
+        k += 1
+        i += 1
+    }
+    
+    while j <= high {
+        array_2[k] = array_1[j]
+        k += 1
+        j += 1
+    }
+    
+    for i in low...high {
+        array_1[i] = array_2[i - low]
+    }
+}
+
+// the recursive sorting algorithm that divides the array, sorts the two halves and merges them
+func sort(_ array: inout [Int], _ low: Int, _ high: Int) {
+    if low < high {
+        let mid = (low + high) / 2
+        sort(&array, low, mid)
+        sort(&array, mid + 1, high)
+        merge(&array, low, mid, high)
+    }
+}