Python: Sort unsorted numbers using Strand sort

Last update on January 06 2025 13:31:23 (UTC/GMT +8 hours)

Write a Python program to sort unsorted numbers using Strand sort.

Strand sort is a recursive sorting algorithm that sorts items of a list into increasing order. It has O(n2) worst time complexity which occurs when the input list is reverse sorted. It has a best case time complexity of O(n) which occurs when the input is a list that is already sorted. Strand sort is not in-place as its space complexity is O(n).

Sample Solution:

Python Code:

#Ref:https://bit.ly/3qW9FIX
import operator
def strand_sort(arr: list, reverse: bool = False, solution: list = None) -> list:
    _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
lst = [4, 3, 5, 1, 2]
print("\nOriginal list:")
print(lst)
print("After applying  Strand sort the said list becomes:")
print(strand_sort(lst))
lst = [5, 9, 10, 3, -4, 5, 178, 92, 46, -18, 0, 7]
print("\nOriginal list:")
print(lst)
print("After applying Strand sort the said list becomes:")
print(strand_sort(lst))
lst = [1.1, 1, 0, -1, -1.1, .1]
print("\nOriginal list:")
print(lst)
print("After applying Strand sort the said list becomes:")
print(strand_sort(lst))

Sample Output:

Original list:
[4, 3, 5, 1, 2]
After applying  Strand sort the said list becomes:
[1, 2, 3, 4, 5]

Original list:
[5, 9, 10, 3, -4, 5, 178, 92, 46, -18, 0, 7]
After applying Strand sort the said list becomes:
[-18, -4, 0, 3, 5, 5, 7, 9, 10, 46, 92, 178]

Original list:
[1.1, 1, 0, -1, -1.1, 0.1]
After applying Strand sort the said list becomes:
[-1.1, -1, 0, 0.1, 1, 1.1]

Flowchart:

Python Code Editor:

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