# What is the best case complexity of quicksort?

Quick sort on average, time complexity is O(n log n) while in worst case, it can be O(n^2) Selection sort, time complexity is O(n^2).

Array Sorting Algorithms

Algorithm Time Complexity Space Complexity
Best Worst
Quicksort Ω(n log(n)) O(log(n))
Mergesort Ω(n log(n)) O(n)
Timsort Ω(n) O(n)

Beside above, what is quick sort complexity? Quick sort on average, time complexity is O(n log n) while in worst case, it can be O(n^2) Selection sort, time complexity is O(n^2).

Considering this, what is the average case complexity of QuickSort?

Quicksort

Animated visualization of the quicksort algorithm. The horizontal lines are pivot values.
Class Sorting algorithm
Worst-case performance O(n2)
Best-case performance O(n log n) (simple partition) or O(n) (three-way partition and equal keys)
Average performance O(n log n)

What is the fastest sorting algorithm?

Quicksort

### Why is QuickSort so fast?

Wikipedia suggests: Typically, quicksort is significantly faster in practice than other O(nlogn) algorithms, because its inner loop can be efficiently implemented on most architectures, and in most real-world data, it is possible to make design choices that minimize the probability of requiring quadratic time.

### Why is QuickSort better than mergesort?

Why quicksort is better than mergesort ? Quick sort is an in-place sorting algorithm. In-place sorting means no additional storage space is needed to perform sorting. Merge sort requires a temporary array to merge the sorted arrays and hence it is not in-place giving Quick sort the advantage of space.

### Is QuickSort a stable algorithm?

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

### What is time complexity of insertion sort?

When analyzing algorithms, the average case often has the same complexity as the worst case. So insertion sort, on average, takes O ( n 2 ) O(n^2) O(n2) time. Insertion sort has a fast best-case running time and is a good sorting algorithm to use if the input list is already mostly sorted.

### Why QuickSort is Nlogn?

Since the input (by definition) isn’t sorted, to partition it like that, it has to look at every item in the input, so that’s an O(N) operation. After it’s partitioned the input the first time, it recursively sorts each of those “chunks”.

### Is merge sort better than quick?

The quick sort is in place as it doesn’t require any additional storage. Efficiency : Merge sort is more efficient and works faster than quick sort in case of larger array size or datasets. Quick sort is more efficient and works faster than merge sort in case of smaller array size or datasets.

### What is time complexity algorithm?

Time complexity of an algorithm quantifies the amount of time taken by an algorithm to run as a function of the length of the input. Similarly, Space complexity of an algorithm quantifies the amount of space or memory taken by an algorithm to run as a function of the length of the input.

n^2

### How do I make a QuickSort stable?

Of course, you can always just go through the array being sorted and add an extra key that is its place in the original array. Then the quicksort will be stable and you just go through and remove the extra key at the end. The condition is easy to figure out, just keep the raw order for equal elements.

n*log(n)

### How does quick sort work?

Quick Sort is a divide and conquer algorithm. It creates two empty arrays to hold elements less than the pivot value and elements greater than the pivot value, and then recursively sort the sub arrays. There are two basic operations in the algorithm, swapping items in place and partitioning a section of the array.

### What is the running time of QuickSort when all elements are same?

What is the running time of Quicksort when all elements of array A have the same value? is T(n) = T(n – 1) + n. By iteration method, T(n) = Θ(n2). Show that the running time of QuickSort is Θ(n2) when the array A contains distinct elements and is sorted in decreasing order.