Data update

Task/Permutations-Derangements/EasyLang/permutations-derangements.easy

@@ -0,0 +1,43 @@
+global list[] rlist[][] .
+proc permlist k . .
+   if k >= len list[]
+      for i to len list[]
+         if i = list[i]
+            return
+         .
+      .
+      rlist[][] &= list[]
+      return
+   .
+   for i = k to len list[]
+      swap list[i] list[k]
+      permlist k + 1
+      swap list[k] list[i]
+   .
+.
+#
+proc derang n . r[][] .
+   rlist[][] = [ ]
+   list[] = [ ]
+   for i to n
+      list[] &= i
+   .
+   permlist 1
+   r[][] = rlist[][]
+.
+r[][] = [ ]
+derang 4 r[][]
+print r[][]
+#
+func subfac n .
+   if n < 2
+      return 1 - n
+   .
+   return (subfac (n - 1) + subfac (n - 2)) * (n - 1)
+.
+#
+print "counted / calculated"
+for n = 0 to 9
+   derang n r[][]
+   print n & ": " & len r[][] & " " & subfac n
+.