lecture-16

# lecture-16 - CPSC 223 Algorithms Data Abstract Structures...

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10/26/10 1 CPSC 223 Algorithms & Data Abstract Structures Lecture 16: Heapsort Today … Quiz 7 Assignments Assignment 7 due Thursday! Note on passing pointers by-reference Heapsort [Sect. 11.2] Heapsort exercise CPSC 223 -­૒-­૒ Fall 2010 2

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10/26/10 2 CPSC 223 -­૒-­૒ Fall 2010 3 Heapsort Heapsort The basic idea: Build a heap out of the unsorted list Create a temporary array Find max value and delete Put max value in last position of temp array Find next max value and delete Put next max value in the next to last position of temp array Repeat until the heap is empty! What is the cost of doing this? O ( n log n ) for building the heap (repeated insertions) O ( n log n ) for repeatedly deleting elements So, O ( n log n ) CPSC 223 -­૒-­૒ Fall 2010 4
10/26/10 3 Heapsort Building the Heap Instead of building a Heap by repeated insertions … We can improve efficiency by: Treating the input array as a heap

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