It’s not going to help you write dotNet stuff at all. I wrote it some time before 2002, and it is insanely complicated, and about 150 lines of code. I don’t think I want to show you that awk code.
#List and recursion using visual prolog 5.2 code
I have some awk code somewhere which may be illustrative - will see if I can locate it. This minimises the size of the arguments being passed around, and also makes them fixed length and so easier to handle. Then just look up the actual strings on output. If your strings can be large, it will usually be more effective to have the recursion work with indexes that relate to the original strings, and construct a set of integer permutations. It can’t recurse any deeper because there is nothing left to work with - it would have to call (list res, List(B, A, D, C), List (null) ) and there is no future in that.Ī level 2 call might receive args (List res, List B, A), List (C, D) and make two level 3 calls that add BACD and BADC. So for example, a level 3 call might receive args (List res, List (B, A, D), List (C) ) and add result BADC. (Obviously, each output has to have 4 strings in, so only the lowest level of recursion can add results to that list.) A reference to a results list to which it can append each fresh permutation as it is identified. Typically, R is passed two other paramaters apart from the remaining list: The hard bit is to combine the pieces down through the structure. the call R(ABD) is going to do (A, BD) which does (B, D) and (D, B), and so on. But if you think of the depth-wise actions, e.g. So on the outer call, R receives the list ABCD. For each element, it retains the current element, and passes a shorter list, excluding that element, to itself. What the function does, is to iterate over the input list. In this case, your initial entry to the recursive function R() is a list of all N strings (4 in this instance).
#List and recursion using visual prolog 5.2 series
Effectively, recursion uses the stack to construct a series of loops whose nesting is calculated at run time, not at coding time. The idea is to reduce the problem by one order of complexity at each level. The universal design for this is Recursion. That’s not exactly a generic design solution. But then, for A B C D E, your code structure would need modification into five loops. So be careful about any code you pick up from the web, in case it does the other one.įour nested loops would address your problem. ABCD has 24 permutations, but only one combination (because order has no significance).įar as I understand it, your examples are actually permutations. Key question is: do you know the difference between permutations and combinations? Wikipedia has good articles on both.
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