all tasks

Task/Sorting-algorithms-Permutation-sort/Go/sorting-algorithms-permutation-sort.go

@@ -0,0 +1,39 @@
+package main
+
+import "fmt"
+
+var a = []int{170, 45, 75, -90, -802, 24, 2, 66}
+
+// in place permutation sort of slice a
+func main() {
+    fmt.Println("before:", a)
+    if len(a) > 1 && !recurse(len(a) - 1) {
+        // recurse should never return false from the top level.
+        // if it does, it means some code somewhere is busted,
+        // either the the permutation generation code or the
+        // sortedness testing code.
+        panic("sorted permutation not found!")
+    }
+    fmt.Println("after: ", a)
+}
+
+// recursive permutation generator
+func recurse(last int) bool {
+    if last <= 0 {
+        // bottom of recursion.  test if sorted.
+        for i := len(a) - 1; a[i] >= a[i-1]; i-- {
+            if i == 1 {
+                return true
+            }
+        }
+        return false
+    }
+    for i := 0; i <= last; i++ {
+        a[i], a[last] = a[last], a[i]
+        if recurse(last - 1) {
+            return true
+        }
+        a[i], a[last] = a[last], a[i]
+    }
+    return false
+}