Quick Sort,take longer

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Why the method quicksort takes longer to sort a vector is a vector ordered than disordered?

Posted 26-Jun-13 3:53am

Bruno Petters

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Maximilien · Answer 1 · 2013-06-26T04:06:00

Quicksort is faster in most cases, except when the vector (in that case) is already sorted.

In the worse case it is O(n2), on average, it is O(n log n) which is what we usually look for when describing algorithms, we look for the best average "complexity" speed, not the worse cases.

If I remember correctly, when an array is sorted, a simple bubble sort will be faster than QuickSort.

Sergey Alexandrovich Kryukov · Answer 2 · 2013-06-26T04:09:00

Solution 2

Because you used the vector ordered the way that the number of sorting operations is more than in an average case of randomly ordered vector. I don't see why it can come at surprise.

—SA

Posted 26-Jun-13 4:09am

Sergey Alexandrovich Kryukov

Comments

Nelek 26-Jun-13 10:43am

Maybe he thought: If already sorted, it should not take so long because it is not needed to move anything.

Sergey Alexandrovich Kryukov 26-Jun-13 11:03am

Yo are right of course, but, for further investigation, one would need an example of sorting: nothing tells me that it's sorted in the required order, it could be some other order (say, reverse). Besides, sorted vector still needs a checkup that it is properly sorted. The sorting algorithm is optimized for sorting starting from the random order.
—SA