Lecture09

Lecture09 - CS2134 Lecture 9: Sorting D N W A s f o S F H n...

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Unformatted text preview: CS2134 Lecture 9: Sorting D N W A s f o S F H n n S w d W t s CS2134 Merge Sort 43 37 25 20 4 15 72 19 4 19 15 72 20 25 43 37 43 37 25 20 4 15 72 19 DIVIDE IN HALF SORT EACH HALF MERGE 4 19 15 72 20 25 43 37 CS2134 QuickSort 43 37 25 20 4 15 72 19 43 37 25 20 4 15 72 19 SELECT PIVOT; PARTITION SORT EACH PIECE (Recursively) 4 19 15 72 20 25 43 37 <= pivot pivot >= pivot done! CS2134 Quick Sort Partition array into two pieces: (elements <= pivot) , (elements >= pivot) Conquer: sort each half recursively Analysis: partition step can be done in linear time Running time depends on choice of pivots at each stage Equal sized piece situation similar to merge sort Very unequal sizes poor performance CS2134 Running Time Worst case: suppose largest element is chosen as pivot on each call to Quicksort: Quicksort(a, 0, n-1) calls Quicksort(a, 0, n-2) calls Quicksort(a, 0, n-3) calls .....
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Lecture09 - CS2134 Lecture 9: Sorting D N W A s f o S F H n...

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