diff --git a/sorts/merge_insertion_sort.py b/sorts/merge_insertion_sort.py new file mode 100644 index 000000000000..339851699525 --- /dev/null +++ b/sorts/merge_insertion_sort.py @@ -0,0 +1,179 @@ +""" +This is a pure Python implementation of the merge-insertion sort algorithm +Source: https://en.wikipedia.org/wiki/Merge-insertion_sort + +For doctests run following command: +python3 -m doctest -v merge_insertion_sort.py +or +python -m doctest -v merge_insertion_sort.py + +For manual testing run: +python3 merge_insertion_sort.py +""" + +from typing import List + + +def merge_insertion_sort(collection: List[int]) -> List[int]: + """Pure implementation of merge-insertion sort algorithm in Python + + :param collection: some mutable ordered collection with heterogeneous + comparable items inside + :return: the same collection ordered by ascending + + Examples: + >>> merge_insertion_sort([0, 5, 3, 2, 2]) + [0, 2, 2, 3, 5] + + >>> merge_insertion_sort([99]) + [99] + + >>> merge_insertion_sort([-2, -5, -45]) + [-45, -5, -2] + """ + + def binary_search_insertion(sorted_list, item): + left = 0 + right = len(sorted_list) - 1 + while left <= right: + middle = (left + right) // 2 + if left == right: + if sorted_list[middle] < item: + left = middle + 1 + break + elif sorted_list[middle] < item: + left = middle + 1 + else: + right = middle - 1 + sorted_list.insert(left, item) + return sorted_list + + def sortlist_2d(list_2d): + def merge(left, right): + result = [] + while left and right: + if left[0][0] < right[0][0]: + result.append(left.pop(0)) + else: + result.append(right.pop(0)) + return result + left + right + + length = len(list_2d) + if length <= 1: + return list_2d + middle = length // 2 + return merge(sortlist_2d(list_2d[:middle]), sortlist_2d(list_2d[middle:])) + + if len(collection) <= 1: + return collection + + """ + Group the items into two pairs, and leave one element if there is a last odd item. + + Example: [999, 100, 75, 40, 10000] + -> [999, 100], [75, 40]. Leave 10000. + """ + two_paired_list = [] + has_last_odd_item = False + for i in range(0, len(collection), 2): + if i == len(collection) - 1: + has_last_odd_item = True + else: + """ + Sort two-pairs in each groups. + + Example: [999, 100], [75, 40] + -> [100, 999], [40, 75] + """ + if collection[i] < collection[i + 1]: + two_paired_list.append([collection[i], collection[i + 1]]) + else: + two_paired_list.append([collection[i + 1], collection[i]]) + + """ + Sort two_paired_list. + + Example: [100, 999], [40, 75] + -> [40, 75], [100, 999] + """ + sorted_list_2d = sortlist_2d(two_paired_list) + + """ + 40 < 100 is sure because it has already been sorted. + Generate the sorted_list of them so that you can avoid unnecessary comparison. + + Example: + group0 group1 + 40 100 + 75 999 + -> + group0 group1 + [40, 100] + 75 999 + """ + result = [i[0] for i in sorted_list_2d] + + """ + 100 < 999 is sure because it has already been sorted. + Put 999 in last of the sorted_list so that you can avoid unnecessary comparison. + + Example: + group0 group1 + [40, 100] + 75 999 + -> + group0 group1 + [40, 100, 999] + 75 + """ + result.append(sorted_list_2d[-1][1]) + + """ + Insert the last odd item left if there is. + + Example: + group0 group1 + [40, 100, 999] + 75 + -> + group0 group1 + [40, 100, 999, 10000] + 75 + """ + if has_last_odd_item: + pivot = collection[-1] + result = binary_search_insertion(result, pivot) + + """ + Insert the remaining items. + In this case, 40 < 75 is sure because it has already been sorted. + Therefore, you only need to insert 75 into [100, 999, 10000], + so that you can avoid unnecessary comparison. + + Example: + group0 group1 + [40, 100, 999, 10000] + ^ You don't need to compare with this as 40 < 75 is already sure. + 75 + -> + [40, 75, 100, 999, 10000] + """ + is_last_odd_item_inserted_before_this_index = False + for i in range(len(sorted_list_2d) - 1): + if result[i] == collection[-i]: + is_last_odd_item_inserted_before_this_index = True + pivot = sorted_list_2d[i][1] + # If last_odd_item is inserted before the item's index, + # you should forward index one more. + if is_last_odd_item_inserted_before_this_index: + result = result[: i + 2] + binary_search_insertion(result[i + 2 :], pivot) + else: + result = result[: i + 1] + binary_search_insertion(result[i + 1 :], pivot) + + return result + + +if __name__ == "__main__": + user_input = input("Enter numbers separated by a comma:\n").strip() + unsorted = [int(item) for item in user_input.split(",")] + print(merge_insertion_sort(unsorted))