stdstablesort

std::stable_sort is a function template in the C++ Standard Library that sorts elements within a specified range while maintaining the relative order of equivalent elements. It is part of the <algorithm> header and provides a stable sorting algorithm, meaning that if two elements are considered equal according to the comparison criterion, their original order in the input sequence is preserved in the output.

The primary advantage of std::stable_sort is its stability, which is particularly important in scenarios where the order of equal elements carries semantic meaning or is relevant for subsequent processing. Unlike std::sort, which may reorder equivalent elements for performance optimization, std::stable_sort guarantees the preservation of original order.

std::stable_sort typically uses a comparison function or predicate that determines the sort order, with the default being std::less, which sorts the elements in ascending order. The function works on iterators defining the range of elements to be sorted, and it rearranges the elements in-place.

The algorithm usually employs a hybrid approach, combining a divide-and-conquer strategy such as merge sort, which provides stability and good worst-case performance, with other sorting methods to optimize efficiency depending on the input data. As a result, std::stable_sort generally has a time complexity of O(n log n), but it may be less performant than std::sort in some cases where stability is not required.

In summary, std::stable_sort is a useful tool in C++ for sorting collections where maintaining the initial relative order of equivalent items is necessary, ensuring predictable and consistent results.