# On what input data does Quicksort exhibit its worst case behavior?

## On what input data does Quicksort exhibit its worst case behavior?

Quicksort has its worst performance, if the pivot is likely to be either the smallest, or the largest element in the list (e.g. the first or last element of an already sorted list). If, e.g. you choose the middle element of the list, an already sorted list does not have the worst case runtime.

What makes quicksort unstable?

A sorting algorithm is said to be stable if it maintains the relative order of records in the case of equality of keys. A stable algorithm produces first output. QuickSort is an unstable algorithm because we do swapping of elements according to pivot’s position (without considering their original positions).

### What are the weaknesses of quicksort?

• It is recursive. Especially, if recursion is not available, the implementation is extremely complicated.
• It requires quadratic (i.e., n2) time in the worst-case.
• It is fragile, i.e. a simple mistake in the implementation can go unnoticed and cause it to perform badly.
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In which of the following cases does Quicksort perform the worst?

Explanation: Fast sort’s worst-case running time is O. (n2). When the partitioning routine generates two sub-arrays, one with n – 1 elements and the other with 0 elements, the worst case behaviour occurs in Fast sort.

## What happens when quicksort performs its worst case?

When Does the Worst Case of Quicksort Occur? elements. Similarly, when the given input array is sorted reversely and we choose the rightmost element as the pivot element, the worst case occurs. Again, in this case, the pivot elements will split the input array into two unbalanced arrays.

What is the best case for quicksort?

n*log(n)
Quicksort/Best complexity

Yes quicksort is not adaptive. Thats the property of quick sort. Quicksort, when its choice of pivots is random, has a runtime of O(n lg n) where n is the size of the array. If its choice of pivots is in sorted order its runtime degrades to O(n^2).

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Is quicksort a stable algorithm?

No
Quicksort/Stable

Disadvantages: 1. Since Radix Sort depends on digits or letters, Radix Sort is much less flexible than other sorts. The constant for Radix sort is greater compared to other sorting algorithms.

What is the disadvantages of selection sort?

What is the disadvantage of selection sort? Explanation: As the input size increases, the performance of selection sort decreases. Explanation: Selection sort is insensitive to input, hence 4(n-1) iterations. Whereas bubble sort iterates only once to set the flag to 0 as the input is already sorted.

### Why is quicksort O N 2 worst case?

The worst case time complexity of a typical implementation of QuickSort is O(n2). The worst case occurs when the picked pivot is always an extreme (smallest or largest) element. This happens when input array is sorted or reverse sorted and either first or last element is picked as pivot.

What is the worst-case behavior for quicksort?

The worst-case behavior for quicksort occurs when the partitioning routine produces one region with n- 1 elements and one with only l element. (This claim is proved in Section 8.4.1.) Let us assume that this unbalanced partitioning arises at every step of the algorithm.

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## What is the running time of quicksort?

The running time of quicksort depends on whether the partitioning is balanced or unbalanced, and this in turn depends on which elements are used for partitioning. If the partitioning is balanced, the algorithm runs asymptotically as fast as merge sort. If the partitioning is unbalanced, however, it can run asymptotically as slow as insertion sort.

Does quicksort use a random number generator?

Section 8.3 presents two versions of quicksort that use a random-number generator. These “randomized” algorithms have many desirable properties. Their average-case running time is good, and no particular input elicits their worst-case behavior.

### What is the difference between quicksort and merge sort?

As in merge sort, the time for a given recursive call on an -element subarray is . In merge sort, that was the time for merging, but in quicksort it’s the time for partitioning.