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Problem with recursion

mario tan

Joined: Mar 09, 2005
Posts: 10
Hi guys,

Ive read an article which talks about recursion and I find it very interesting. However my mind boggles everytime I read the code from this article:

Connect 4 recursion

Please take time to look at the code..

You can see there that each time the method best_move is called, there is always that declaration and instantiation of best_score.

best_score is an instance of MoveValue.

Since this is a recursive method, will each call to the method best_move have its own copy of best_score? That means that there could be plenty of MoveValue object that will reside on the heap having only one name which is best_score?

I've tested the code but the best_move always return a MoveValue object with score = 0 and col = 6.

Why is that so?.. Can someone please explain to me the code and how to correctly trace it? Thanks in advance.

Best regards,

fred rosenberger
lowercase baba

Joined: Oct 02, 2003
Posts: 11877

I didn't look at the code, but the answer is probably yes.

when a method is called, any method variables get created. it doesn't matter who calls the method, a new set get created.

so, if you have a method call itself, the top level will have a copy, the next level will have its own copy, and so on, all the way down.

technically, object on the heap do not have names. if your method has a "best_score" variable, you actually have two things. you have the object itself that lives on the heap, and the REFERENCE named "best_score". the reference lives on the stack, and knows where its best_score object lives. each new 'best_score' reference hides all the previous ones, and the current one points to the current object.

There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
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subject: Problem with recursion
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