10-recursion

# 10-recursion - CSE143 Lecture10 Recursion...

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CSE 143 Lecture 10 Recursion slides created by Marty Stepp and Alyssa Harding http://www.cs.washington.edu/143/

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2 Recursion Iteration : a programming technique in which you describe  actions to be repeated using a loop Recursion : a programming technique in which you describe  actions to be repeated using a method that calls itself Both approaches can be used to solve the same problems Some problems are easier solved  iteratively Some problems are easier solved  recursively Sometimes the recursive solution is a LOT simpler than the  iterative solution!
3 Exercise How many students total are directly behind you in your  "column" of the classroom? You have poor vision, so you can see only the people right next to you. So you can't just look back and count. But you are allowed to ask questions of the person next to you. How can we solve this problem? ( recursively  )

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4 The idea Recursion is all about breaking a big problem into smaller  occurrences of that same problem. Each person can solve a small part of the problem. What is a small version of the problem that would be easy to answer? What information from a neighbor might help me?
5 Recursive algorithm Number of people behind me: If there is someone behind me, ask him/her how many people are behind him/her. When they respond with a value  N , then I will answer  N + 1 . If there is nobody behind me, I will answer  0 .

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6 Recursion and cases Every recursive algorithm involves at least 2 cases: base case : A simple occurrence that can be answered directly. recursive case : A more complex occurrence of the problem that  cannot be directly answered, but can instead be described in  terms of smaller occurrences of the same problem. Some recursive algorithms have more than one base or recursive
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10-recursion - CSE143 Lecture10 Recursion...

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