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CS 240: Data Structures

CS 240: Data Structures. Thursday, July 12 th Sorting – Bubble, Insertion, Quicksort, Mergesort, Analysis, STL. Sorting. Ok, so we have a list:. X1, X2, X3, X4, X5, X6, … XN. We can sort this list either ascending or descending. Protip: You only need operator < .

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CS 240: Data Structures

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  1. CS 240: Data Structures Thursday, July 12th Sorting – Bubble, Insertion, Quicksort, Mergesort, Analysis, STL

  2. Sorting • Ok, so we have a list: X1, X2, X3, X4, X5, X6, … XN • We can sort this list either ascending or descending. • Protip: You only need operator <. • Not that I want you to code any less. I like it when you write operator > too.

  3. Sorting • First, we describe some simple techniques. • These techniques are usually slow (O(n2)) • But, they are easier to understand. • You will have to understand the more complex schemes eventually. There is no escape. http://tanksoftware.com/tutes/uni/sorting.html

  4. Insertion Sort • There are two kinds of insertion sort: • Insert in-order into a new list • Reposition into our existing array • What are the tradeoffs?

  5. Insertion Sort

  6. Bubble Sort • Has a good name. • Easy to understand. • Slow and crusty. • What is its efficiency?

  7. Sorts • Ok, now that I’ve filled your head with the basics. Do you want to know the ultimate, mega-powered, best sort ever? • Me too. I like quicksort though. • Too many variables apply: • List contents • Pre-sortedness • Etc.

  8. Mergesort • Mergesort takes two (or more) inputs and sorts them! • But how? • By insertion! • Uh oh… everyone has to get up now.

  9. Quicksort • The “Bad Boy” of sorts. • This is recursive too. • Again, everyone needs to get up. • Hey…. These slides are pretty empty. But, you get to code this stuff!

  10. Radix Sort • Sorting by digits… maybe characters… • Lets create some 3-digit numbers. • What if our numbers don’t have the same number of digits? • Lexigraphical order?

  11. Sorts • Sort of a randomly generated list of 500 items • Times are based on 70’s hardware • (we have faster computers now) Booya!

  12. STL sort • In order to use the STL sort, you need to use iterators! • We’ll use vector to do this! • Remind me to put this code online.

  13. Sort Analysis • Well, first we need to explain more structurally how these work: • Mergesort: • Split up a list into smaller parts (half size) until the list is of size 1. • Put lists back together by “merging”: insertion sort • Quicksort: • Select a value and ensure that all values to the left are smaller – all values to the right are equal or larger • Repeat with left/right side until they are of size 1 or 2 (and sorted).

  14. Indirect Sorting • Well, remember the difference between pass by value and pass by reference in terms of speed? • Sometimes you need to sort large objects! • You can use pointers! Fast access! Avoid copying data around!

  15. Next week… • Presentations on Tuesday. • Second exam on Thursday! Yay! + 1

  16. Searches! • Linear search • You know this, you know you do. • Binary search • Why is this a problem with linked list? • Next time: Hashes!

  17. Project 2 • Recursion time!

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