Data commit

Task/Permutations-by-swapping/FreeBASIC/permutations-by-swapping.basic

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+' version 31-03-2017
+' compile with: fbc -s console
+
+Sub perms(n As ULong)
+
+    Dim As Long p(n), i, k, s = 1
+
+    For i = 1 To n
+        p(i) = -i
+    Next
+
+    Do
+        Print "Perm: [ ";
+        For i = 1 To n
+            Print Abs(p(i)); " ";
+        Next
+        Print "] Sign: "; s
+
+        k = 0
+        For i = 2 To n
+            If p(i) < 0 Then
+                If Abs(p(i)) > Abs(p(i -1)) Then
+                    If Abs(p(i)) > Abs(p(k)) Then k = i
+                End If
+            End If
+        Next
+
+        For i = 1 To n -1
+            If p(i) > 0 Then
+                If Abs(p(i)) > Abs(p(i +1)) Then
+                    If Abs(p(i)) > Abs(p(k)) Then k = i
+                End If
+            End If
+        Next
+
+        If k Then
+            For  i = 1 To n
+                If Abs(p(i)) > Abs(p(k)) Then p(i) = -p(i)
+            Next
+            i = k + Sgn(p(k))
+            Swap p(k), p(i)
+            s = -s
+        End If
+
+    Loop Until k = 0
+
+End Sub
+
+' ------=< MAIN >=------
+
+perms(3)
+print
+perms(4)
+
+' empty keyboard buffer
+While Inkey <> "" : Wend
+Print : Print "hit any key to end program"
+Sleep
+End