Another update from ingydotnet^djgoku

Task/Permutations-by-swapping/PowerShell/permutations-by-swapping.psh

@@ -0,0 +1,42 @@
+function permutation ($array) {
+    function sign($A) {
+        $size = $A.Count
+        $sign = 1
+        for($i = 0; $i -lt $size; $i++) {
+            for($j = $i+1; $j -lt $size ; $j++) {
+                if($A[$j] -lt $A[$i]) { $sign *= -1}
+            }
+        }
+        $sign
+    }
+    function generate($n, $A, $i1, $i2, $cnt) {
+        if($n -eq 1) {
+            if($cnt -gt 0) {
+                "$A -- swapped positions: $i1 $i2 -- sign = $(sign $A)`n"
+            } else {
+                "$A -- sign = $(sign $A)`n"
+            }
+        }
+        else{
+            for( $i = 0; $i -lt ($n - 1); $i += 1) {
+                generate ($n - 1) $A $i1 $i2 $cnt
+                if($n % 2 -eq 0){
+                    $i1, $i2 = $i, ($n-1)
+                    $A[$i1], $A[$i2] = $A[$i2], $A[$i1]
+                    $cnt = 1
+                }
+                else{
+                    $i1, $i2 = 0, ($n-1)
+                    $A[$i1], $A[$i2] = $A[$i2], $A[$i1]
+                    $cnt = 1
+                }
+            }
+            generate ($n - 1) $A $i1 $i2 $cnt
+        }
+    }
+    $n = $array.Count
+    if($n -gt 0) {
+        (generate $n $array  0 ($n-1) 0)
+    } else {$array}
+}
+permutation @(1,2,3,4)