March 2014 update

Task/Sorting-algorithms-Quicksort/Go/sorting-algorithms-quicksort-2.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+    "fmt"
+    "sort"
+    "math/rand"
+)
+
+func partition(a sort.Interface, first int, last int, pivotIndex int) int {
+    a.Swap(first, pivotIndex) // move it to beginning
+    left := first+1
+    right := last
+    for left <= right {
+        for left <= last && a.Less(left, first) {
+            left++
+        }
+        for right >= first && a.Less(first, right) {
+            right--
+        }
+        if left <= right {
+            a.Swap(left, right)
+            left++
+            right--
+        }
+    }
+    a.Swap(first, right) // swap into right place
+    return right
+}
+
+func quicksortHelper(a sort.Interface, first int, last int) {
+    if first >= last {
+        return
+    }
+    pivotIndex := partition(a, first, last, rand.Intn(last - first + 1) + first)
+    quicksortHelper(a, first, pivotIndex-1)
+    quicksortHelper(a, pivotIndex+1, last)
+}
+
+func quicksort(a sort.Interface) {
+    quicksortHelper(a, 0, a.Len()-1)
+}
+
+func main() {
+    a := []int{1, 3, 5, 7, 9, 8, 6, 4, 2}
+    fmt.Printf("Unsorted: %v\n", a)
+    quicksort(sort.IntSlice(a))
+    fmt.Printf("Sorted: %v\n", a)
+    b := []string{"Emil", "Peg", "Helen", "Juergen", "David", "Rick", "Barb", "Mike", "Tom"}
+    fmt.Printf("Unsorted: %v\n", b)
+    quicksort(sort.StringSlice(b))
+    fmt.Printf("Sorted: %v\n", b)
+}