CS102_Recursion

CS102_Recursion - CS102Recursion DavidDavenport...

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CS102 – Recursion David Davenport Bilkent University Ankara – Turkey email: [email protected] Spring 2003

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What is Recursion? Method of solving problems Alternative to iteration All recursive solutions  can be implemented iteratively Characteristic... recursive methods call themselves recursive functions defined in terms of  (simpler versions) themselves General recursive case  & stopping cases
Factorial N Iterative N! = N * N-1 * N-2 … 2 * 1 Recursive 1! = 1  - stopping case N! = N * (N-1)! - general case implement & trace in Java

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So, why use recursion? Advantages... Interesting conceptual framework Intuitive solutions to difficult problems But, disadvantages... requires more memory & time requires different way of thinking!
Towers of Hanoi The Problem… Rules only move one disk at a time can’t put a disk on a smaller one Monks believed world would end  once solved for 64 disks! Takes 580 billion years!  at one move per sec.

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Print reverse Print first N values in reverse Simple iterative solution… Recursive? Hint - what is the simplest case? Write out sequence of cases & look for previous case within each case generalise & note stopping case!
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