import operator def strand_sort(arr: list, reverse: bool = False, solution: list = None) -> list: """ Strand sort implementation source: https://en.wikipedia.org/wiki/Strand_sort :param arr: Unordered input list :param reverse: Descent ordering flag :param solution: Ordered items container Examples: >>> strand_sort([4, 2, 5, 3, 0, 1]) [0, 1, 2, 3, 4, 5] >>> strand_sort([4, 2, 5, 3, 0, 1], reverse=True) [5, 4, 3, 2, 1, 0] """ _operator = operator.lt if reverse else operator.gt solution = solution or [] if not arr: return solution sublist = [arr.pop(0)] for i, item in enumerate(arr): if _operator(item, sublist[-1]): sublist.append(item) arr.pop(i) # merging sublist into solution list if not solution: solution.extend(sublist) else: while sublist: item = sublist.pop(0) for i, xx in enumerate(solution): if not _operator(item, xx): solution.insert(i, item) break else: solution.append(item) strand_sort(arr, reverse, solution) return solution if __name__ == "__main__": assert strand_sort([4, 3, 5, 1, 2]) == [1, 2, 3, 4, 5] assert strand_sort([4, 3, 5, 1, 2], reverse=True) == [5, 4, 3, 2, 1]