# Which sorting is stable?

## Which sorting is stable?

Several common sorting algorithms are stable by nature, such as Merge Sort, Timsort, Counting Sort, Insertion Sort, and Bubble Sort. Others such as Quicksort, Heapsort and Selection Sort are unstable. We can modify unstable sorting algorithms to be stable.

## Is Qsort a stable sort?

No
Quicksort/Stable
Since quicksort is an unstable sort — there are multiple possible results when the array contains equivalent elements — this means qsort() is not guaranteed to be stable, even if internally the C library is using a stable sort like merge sort. The C standard library has no stable sort function.

What does it mean if a sort is stable?

A sorting algorithm is stable if it preserves the order of duplicate keys. The trouble is, if we sort the same data according to one key, and then according to a second key, the second key may destroy the ordering achieved by the first sort. But this will not happen if our second sort is a stable sort.

Is STL sort stable?

As of September 2020, it appears that libc++ std::sort happens to be stable for all ranges of size less than 31, and libstdc++ std::sort happens to be stable for all ranges of size less than 17. (Do not rely on this little factoid in production!)

### What is stable sort example?

Stable sorting algorithm A sorting algorithm is said to be stable if the order of the same values in the output remains the same as in input array. This is an example of stable sorting, element 12 appears twice at index 5 and at index 7.

### Is Python sorted stable?

The built-in sorted() function is guaranteed to be stable. A sort is stable if it guarantees not to change the relative order of elements that compare equal — this is helpful for sorting in multiple passes (for example, sort by department, then by salary grade).

Heap sort is not stable because operations in the heap can change the relative order of equivalent keys. The binary heap can be represented using array-based methods to reduce space and memory usage. Heap sort is an in-place algorithm, where inputs are overwritten using no extra data structures at runtime.

Is quicksort divide and conquer?

Like merge sort, quicksort uses divide-and-conquer, and so it’s a recursive algorithm. The way that quicksort uses divide-and-conquer is a little different from how merge sort does.

## How does count sort work?

Counting sort works by iterating through the input, counting the number of times each item occurs, and using those counts to compute an item’s index in the final, sorted array.

## Is C++ sort fast?

C++ sort() is blazingly faster than qsort() on equivalent data due to inlining. sort() on a container of integers will be compiled to use std::less ::operator() by default, which will be inlined and sort() will be comparing the integers directly.

Is C++ sort function stable?

sort() function usually uses Introsort. Therefore, sort() may preserve the physical order of semantically equivalent values but can’t be guaranteed. stable_sort() function usually uses mergesort. Therefore, stable_sort() preserve the physical order of semantically equivalent values and its guaranteed.

How can I perform a stable sort with Q sort?

The only way to perform a stable sort with qsort is to first augment the objects with a monotonic counter of some kind. Here is a simple example of sorting an array of doubles in numerical order, using the comparison function defined above (see Comparison Functions ):

### What is the difference between stable_sort and sort in Python?

Sorts the elements in the range [first,last) into ascending order, like sort, but stable_sort preserves the relative order of the elements with equivalent values. The elements are compared using operator< for the first version, and comp for the second.

### What is the difference between compare_as_ints and stable_sort?

The function shall not modify any of its arguments. This can either be a function pointer or a function object. compare_as_ints is a function that compares only the integral part of the elements, therefore, elements with the same integral part are considered equivalent. stable_sort preserves the relative order these had before the call.

How can I sort an array of doubles in numerical order?

Here is a simple example of sorting an array of doubles in numerical order, using the comparison function defined above (see Comparison Functions ): The qsort function derives its name from the fact that it was originally implemented using the “quick sort” algorithm.