What are the best sorting algorithms in C?

Often while writing an application, you would need to optimize the code. Not often optimization is required almost every time because no one wants to wait while your program keeps executing. Now, these algorithms are often dependent on how fast you can get work done, like holding a block of data sorted which is getting updated now and then. Sorting algorithms are some of the most common algorithms that can be found in the programming world. Many other algorithms depend on a sorted list of data to function correctly.

But you would even want your sorting algorithms to be optimized to give you the best results. That is why people keep on asking from time to time what the best sorting algorithms are in C? Which sorting algorithms would provide the best results? Almost always the question cannot be answered unambiguously. The speed would depend on a lot of factors. It would heavily depend on the environment where the sorting is done. This means the underlying architecture and the processor has a lot of roles to play in this along with the associated hardware. There are others that would affect the search as well. These include the items that are being sorted. For instance, if you are working with reference data types, you would be working with the addresses instead of actual swapping, while that might not be the case with the primitive data types. This means that there would be a noticeable difference in speeds. Before starting with sorting intricacies, if you are new to C programming then first learn c from the best C tutorials recommended on Hackr.io.

The distribution of the items can be said to be the most significant factor that affects the speed. The algorithms might produce vastly different results on the same dataset with different distribution. That means a lot needs to be kept in mind while dealing with the sorting algorithms in C to determine which one needs to be chosen for a particular purpose.

Sorting a database which is pretty huge (one that cannot be fit into memory at a time) is entirely different from sorting a set of 100 integers. It will not only be so that the implementations would be entirely different; there are chances that an algorithm which is pretty fast in one of the cases would be very costly in terms of time for the other one. Similarly, it can be said that sorting an array is entirely different from sorting a linked list.

Let us find out what are some of the best sorting algorithms in C and how could they be implemented. Let us look at the individual sorting algorithms and find out how fast each of them is and if they could be used in a particular case. The following comparisons would help to understand which algorithms could be used for a specific scenario.

Insertion sort using C

Insertion sort is one of those algorithms which are quite easy to implement and give good results. The best case of the sorting algorithms is perfect and can sort datasets in O(n) time. However, the performance decreases with bigger datasets and with unfriendly distributions. The algorithm works well for small arrays only. The smaller an array is, the faster insertion sort would be than any other algorithm. But, since there is a square term in its complexity, the algorithm would become very slow very quick as the size of the array increases. If the sorting array is tested, it can be seen that it performs well for datasets that have less than 100 integers or characters. But if the size of the array becomes more than 100, the effectiveness of the algorithm starts to decrease.

Shell sort using C

The shell sort is a rather queer algorithm. This is because even though it is quite a good alternative at times, it is different from the other fast sorting algorithms. The complexity is not O(n log n) like the other algorithms. The complexity lies somewhere between O(n log2n) and O(n1.5). It depends on how the algorithm is implemented and others. The shell sort is an in-place and non-recursive algorithm. Its performance is at par with the other sorting algorithms in C. That is why it would be an excellent choice to consider.

Quicksort using C

The next algorithm that should be considered is the quicksort. It can be said to be the most popular sorting algorithm. A library implementation of the quicksort can also be found in C. The virtue of the quicksort is that it sorts in-place and it is a recursive algorithm. It is usually very fast. The inner loop is short and can be optimized well. This makes quicksort perform very well in specific scenarios.

However, the problem with quicksort is that the sorting algorithm cannot be trusted. The worst-case running time comes down to a meager O(n2). It becomes slow and can even be more time-consuming than insertion sort. These cases might pop up without warning, and the problem might also persist if an optimized version of the quicksort is used. The optimized versions often use the median values of the first, last and middle elements as the pivot element and as the sizes of the partitions fall below a certain predefined number, insertion sort is used which is the fastest for such small collections.

An array of sorted values is the worst case for a quicksort, and it ruins the overall performance of the quicksort. It is not just the case with the regular version, but also the optimized program. Vast arrays of such a form will be a total massacre if the quicksort is used. That is why, though the quicksort is a very nice algorithm in best and ordinary cases, and the worst-case performance is not at all satisfiable.

Heap sort using C

Heap sort is a very popular sorting algorithm and is used very frequently. It is an in-place non-recursive sorting algorithm. Though heap sort is not the fastest sorting algorithm for many test cases, it is the sorting algorithm of choice, the de-facto sorting algorithm to ensure that the sorting time would not go any higher than O(n log n). Heap sort is generally appreciated because the algorithm is very trustworthy. There isn’t any such distribution that would cause it to become exceptionally slow. The non-recursive sorting technique also ensures that the algorithm would take no extra memory. This is a very nice feature of this algorithm, which makes it useful in the majority of cases.

Heap sort is thus the sorting algorithm of choice if you would want an algorithm to be handling all types of data collections. It would work pretty well in all situations and never put you in any worry no matter what the case is. It covers all the boundary conditions, and there is no shortcoming. But there can be particular cases where other algorithms would work much faster than heap sort.

Merge sort using C

The virtue of the merge sort implementation in C is that it is a very stable algorithm and it has a truly O(n log n) running time. It does not change the order of equal times even if heap sort could do that. One of the main problems, however, is that it is not economical in terms of size. It requires a second array having the same size as the input array. This means that the memory requirements would be doubled and if the size of the data collection is enormous, it can be understood that it would be challenging to manage memory resources.  This shortcoming of size in terms of the memory requirements could be eased up to a point by passing pointer arguments so that memory does not need to be allocated and deallocated every time. Also, the merging technique could be improved, and the overall performance would surely be quite improved.

Considering all the implementations of the sorting algorithms in C, it is difficult to say which one would be the most useful. There could be thousands of different distributions and boundary cases of various sizes that might cause the algorithms to fail or work exceedingly fast. All these algorithms do give impressive results in different scenarios, and the optimized sorting algorithms that are found in the libraries often use more than one single algorithm. The enhanced quicksort algorithm which can be located in many libraries use insertion sort and heap sort to overcome its shortcomings.

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