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Recursion

Will Myers
Ranch Hand

Joined: Aug 05, 2009
Posts: 326

I was wondering if anyone had a good simple explanation of how to work out what the result is from a recursive method? For example the following produces 24 as the result when you pass in 4... (1 * 2 * 3 * 4 = 24)



but how would you break it down if presented with this sort of question in an interview?

Another example would be


which will return 28 if you pass in 3 and 4 as the args but again how would you work this out manually? Is there a standard formula for breaking these down?
fred rosenberger
lowercase baba
Bartender

Joined: Oct 02, 2003
Posts: 11312
    
  16

paper and pencil is what I would do. if you pass in 3 and 4, it would return

(3 + 4) * recursion(2,2)

that would return

(3+4) * ( (2+2)* (recursion(1,0) )

that would return

(3 + 4) * ( (2+2) * 1)


There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
Ulf Dittmer
Marshal

Joined: Mar 22, 2005
Posts: 41839
    
  63
Either that, or just follow the link.


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Will Myers
Ranch Hand

Joined: Aug 05, 2009
Posts: 326

thanks Fred!

Nice work Ulf
 
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subject: Recursion