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* from __future__ import annotations
* fixup! from __future__ import annotations
* fixup! from __future__ import annotations
* fixup! Format Python code with psf/black push
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74 lines
2.0 KiB
Python
74 lines
2.0 KiB
Python
"""
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Implementation of iterative merge sort in Python
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Author: Aman Gupta
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For doctests run following command:
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python3 -m doctest -v iterative_merge_sort.py
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For manual testing run:
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python3 iterative_merge_sort.py
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"""
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from __future__ import annotations
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def merge(input_list: list, low: int, mid: int, high: int) -> list:
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"""
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sorting left-half and right-half individually
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then merging them into result
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"""
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result = []
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left, right = input_list[low:mid], input_list[mid : high + 1]
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while left and right:
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result.append((left if left[0] <= right[0] else right).pop(0))
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input_list[low : high + 1] = result + left + right
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return input_list
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# iteration over the unsorted list
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def iter_merge_sort(input_list: list) -> list:
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"""
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Return a sorted copy of the input list
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>>> iter_merge_sort([5, 9, 8, 7, 1, 2, 7])
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[1, 2, 5, 7, 7, 8, 9]
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>>> iter_merge_sort([6])
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[6]
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>>> iter_merge_sort([])
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[]
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>>> iter_merge_sort([-2, -9, -1, -4])
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[-9, -4, -2, -1]
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>>> iter_merge_sort([1.1, 1, 0.0, -1, -1.1])
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[-1.1, -1, 0.0, 1, 1.1]
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>>> iter_merge_sort(['c', 'b', 'a'])
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['a', 'b', 'c']
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>>> iter_merge_sort('cba')
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['a', 'b', 'c']
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"""
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if len(input_list) <= 1:
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return input_list
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input_list = list(input_list)
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# iteration for two-way merging
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p = 2
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while p < len(input_list):
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# getting low, high and middle value for merge-sort of single list
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for i in range(0, len(input_list), p):
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low = i
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high = i + p - 1
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mid = (low + high + 1) // 2
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input_list = merge(input_list, low, mid, high)
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# final merge of last two parts
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if p * 2 >= len(input_list):
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mid = i
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input_list = merge(input_list, 0, mid, len(input_list) - 1)
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p *= 2
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return input_list
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if __name__ == "__main__":
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user_input = input("Enter numbers separated by a comma:\n").strip()
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unsorted = [int(item.strip()) for item in user_input.split(",")]
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print(iter_merge_sort(unsorted))
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