The interval between the elements is gradually decreased based on the sequence used. It sorts the elements of a container in the range pointed by the specified iterators using a comparator. It can also be useful when input array is almost sorted, only few elements are misplaced in complete big array. In INSERTION-SORT, the best case occurs if the array is already sorted. So if we have a=2, b=2. With this algorithm, the array is sorted at a specific interval based on the chosen sequence. The default comparator used is std::less> which sorts the container in ascending order using operator<. At the end of the day though, whatever the best sorting algorithm really is depends on the input (and who you ask). In Merge sort, we divide the array recursively in two halves, until each sub-array contains a single element, and then we merge the sub-array in a way that it results into a sorted array. Shell Sort is a variation of Insertion Sort. In the most general case, you'd go with an algorithm that happens to have the best average or best worst-case number of comparisons. The general goal of a sorting algorithm is to minimize the number of comparisons. Sorting algorithms have a lower bound and an upper bound on the number of comparisons( n log n worst-case for merge and heap sorts, n log n average case for quick sort). Example: Gif from GfyCat Code: Uses: Insertion sort is used when number of elements is small. And it takes minimum time (Order of n) when elements are already sorted. The performance of the shell sort depends on the type of sequence used for a given input array. Similor to merge sort, Quicksort works on the divide and conquer algorithm. Boundary Cases: Insertion sort takes maximum time to sort if elements are sorted in reverse order. The merge step takes O(n) memory, so k=1. ; Sorting In place: Yes.It does not uses extra space to sort the elements. To sort an array in reverse/decreasing order, you can use std::sort algorithm provided by STL. The answer, as is often the case for such questions, is "it depends". Quicksort is one of the most efficient ways of sorting elements in computer systems. Average and Worst case sorting occurs when arrays are reverse sorted, Best case sorting occurs when arrays are already sorted. If you want the best sorting algorithm that runs under assumption that âthe data is already sortedâ, then the best algorithm is âdo nothingâ which runs in no time. Mergesort is up there with the fastest standard sort algorithms. If you don't care about memory, a simple Mergesort would suffice. Merge Sort is one of the best examples of Divide & Conquer algorithm. Quick Sort Algorithm. Stable: Yes.It is stable sorting algorithm. Due to its simplicity, it is always used to introduce the concept of sorting. 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