Initial data commit

Task/Sorting-algorithms-Merge-sort/Go/sorting-algorithms-merge-sort.go

@@ -0,0 +1,44 @@
+package main
+
+import "fmt"
+
+var a = []int{170, 45, 75, -90, -802, 24, 2, 66}
+var s = make([]int, len(a)/2+1) // scratch space for merge step
+
+func main() {
+    fmt.Println("before:", a)
+    mergeSort(a)
+    fmt.Println("after: ", a)
+}
+
+func mergeSort(a []int) {
+    if len(a) < 2 {
+        return
+    }
+    mid := len(a) / 2
+    mergeSort(a[:mid])
+    mergeSort(a[mid:])
+    if a[mid-1] <= a[mid] {
+        return
+    }
+    // merge step, with the copy-half optimization
+    copy(s, a[:mid])
+    l, r := 0, mid
+    for i := 0; ; i++ {
+        if s[l] <= a[r] {
+            a[i] = s[l]
+            l++
+            if l == mid {
+                break
+            }
+        } else {
+            a[i] = a[r]
+            r++
+            if r == len(a) {
+                copy(a[i+1:], s[l:mid])
+                break
+            }
+        }
+    }
+    return
+}