## Python, sort, iterative_merge_sort.py

``````"""
Implementation of iterative merge sort in Python
Author: Aman Gupta

For doctests run following command:
python3 -m doctest -v iterative_merge_sort.py

For manual testing run:
python3 iterative_merge_sort.py
"""

from __future__ import annotations

def merge(input_list: list, low: int, mid: int, high: int) -> list:
"""
sorting left-half and right-half individually
then merging them into result
"""
result = []
left, right = input_list[low:mid], input_list[mid : high + 1]
while left and right:
result.append((left if left[0] <= right[0] else right).pop(0))
input_list[low : high + 1] = result + left + right
return input_list

# iteration over the unsorted list
def iter_merge_sort(input_list: list) -> list:
"""
Return a sorted copy of the input list

>>> iter_merge_sort([5, 9, 8, 7, 1, 2, 7])
[1, 2, 5, 7, 7, 8, 9]
>>> iter_merge_sort([6])
[6]
>>> iter_merge_sort([])
[]
>>> iter_merge_sort([-2, -9, -1, -4])
[-9, -4, -2, -1]
>>> iter_merge_sort([1.1, 1, 0.0, -1, -1.1])
[-1.1, -1, 0.0, 1, 1.1]
>>> iter_merge_sort(['c', 'b', 'a'])
['a', 'b', 'c']
>>> iter_merge_sort('cba')
['a', 'b', 'c']
"""
if len(input_list) <= 1:
return input_list
input_list = list(input_list)

# iteration for two-way merging
p = 2
while p < len(input_list):
# getting low, high and middle value for merge-sort of single list
for i in range(0, len(input_list), p):
low = i
high = i + p - 1
mid = (low + high + 1) // 2
input_list = merge(input_list, low, mid, high)
# final merge of last two parts
if p * 2 >= len(input_list):
mid = i
input_list = merge(input_list, 0, mid, len(input_list) - 1)
p *= 2

return input_list

if __name__ == "__main__":
user_input = input("Enter numbers separated by a comma:\n").strip()
unsorted = [int(item.strip()) for item in user_input.split(",")]
print(iter_merge_sort(unsorted))
``````