Recursion Check

I have an item with a name, which runs a recursive routine. Part of that execution involves the possible 'running' of other items of the same type.

I need to check that the recusion is not infinite (i.e. an item will never run itself). The nesting is unlimited.

Is there an efficient algorithm to check this? I can build up the list of the item names, and I'd want to exit if a name is already in the list, but the checking could make this prohibitive time-wise.

Is it quicker to build the whole name list and then check for multiple entries? Or check after each addition?

Or is there a better way?

Any suggestions?

Create an enum of names, then create a simple global array with that many elements, set them all to zero.

Code:

---

Public enum names
    name1
    name2
    ... ad nauseum
end enum
Public arr(100) as Integer
For x = 0 to  name64
    arr(x)=0
next x
..............

'as each name comes up
'  check to see
if arr(name) >0 then
    Exit Sub ' quit the alogorithm
else
      arr(name )=1
end if

---

I don't know how many names there will be before hand, or what they will be. I can only evaluate the list at run time (i.e. it is user configurable).

Any item can refer to up to 10 other item names, which I can look up.

Actually, each item has a unique index (from 1 to 3000). Can I somehow use a MOD to check if that index is already present...

Code:

---

(pseudocode)
Type Item
  Name As String * 10
  Index As Long
  Ref(10) As Item
End Type

---

Its a puzzle. I can do it the hard way, but I'm looking for the quickest...

I used a boolean array recently to check if a node on a tree had been dealt with.

VB Code:

Public Trail() as Boolean
....
....
....
 
NumNodes = LoadTree(Filename") 'returns number of nodes unsurprisingly!
 
Redim Trail(1 to NumNodes) as Boolean
....
....
....
 
'inside recursive function
if Trail(Whatever) then
CollapseRecursion = True 'a public flag to kill recursion upon finding a repetition.
Else
DealWith(Whatever)
End If