Data commit

Task/Permutations-by-swapping/Icon/permutations-by-swapping.icon

@@ -0,0 +1,30 @@
+procedure main(A)
+    every write("Permutations of length ",n := !A) do
+       every p := permute(n) do write("\t",showList(p[1])," -> ",right(p[2],2))
+end
+
+procedure permute(n)
+    items := [[]]
+    every (j := 1 to n, new_items := []) do {
+        every item := items[i := 1 to *items] do {
+            if *item = 0 then put(new_items, [j])
+            else if i%2 = 0 then
+                every k := 1 to *item+1 do {
+                    new_item := item[1:k] ||| [j] ||| item[k:0]
+                    put(new_items, new_item)
+                    }
+            else
+                every k := *item+1 to 1 by -1 do {
+                    new_item := item[1:k] ||| [j] ||| item[k:0]
+                    put(new_items, new_item)
+                    }
+            }
+       items := new_items
+       }
+    suspend (i := 0, [!items, if (i+:=1)%2 = 0 then 1 else -1])
+end
+
+procedure showList(A)
+    every (s := "[") ||:= image(!A)||", "
+    return s[1:-2]||"]"
+end