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* Pyupgrade to Python 3.9
* updating DIRECTORY.md
Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
113 lines
2.9 KiB
Python
113 lines
2.9 KiB
Python
from __future__ import annotations
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def merge(left_half: list, right_half: list) -> list:
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"""Helper function for mergesort.
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>>> left_half = [-2]
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>>> right_half = [-1]
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>>> merge(left_half, right_half)
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[-2, -1]
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>>> left_half = [1,2,3]
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>>> right_half = [4,5,6]
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>>> merge(left_half, right_half)
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[1, 2, 3, 4, 5, 6]
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>>> left_half = [-2]
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>>> right_half = [-1]
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>>> merge(left_half, right_half)
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[-2, -1]
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>>> left_half = [12, 15]
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>>> right_half = [13, 14]
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>>> merge(left_half, right_half)
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[12, 13, 14, 15]
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>>> left_half = []
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>>> right_half = []
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>>> merge(left_half, right_half)
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[]
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"""
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sorted_array = [None] * (len(right_half) + len(left_half))
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pointer1 = 0 # pointer to current index for left Half
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pointer2 = 0 # pointer to current index for the right Half
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index = 0 # pointer to current index for the sorted array Half
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while pointer1 < len(left_half) and pointer2 < len(right_half):
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if left_half[pointer1] < right_half[pointer2]:
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sorted_array[index] = left_half[pointer1]
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pointer1 += 1
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index += 1
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else:
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sorted_array[index] = right_half[pointer2]
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pointer2 += 1
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index += 1
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while pointer1 < len(left_half):
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sorted_array[index] = left_half[pointer1]
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pointer1 += 1
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index += 1
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while pointer2 < len(right_half):
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sorted_array[index] = right_half[pointer2]
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pointer2 += 1
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index += 1
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return sorted_array
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def merge_sort(array: list) -> list:
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"""Returns a list of sorted array elements using merge sort.
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>>> from random import shuffle
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>>> array = [-2, 3, -10, 11, 99, 100000, 100, -200]
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>>> shuffle(array)
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>>> merge_sort(array)
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[-200, -10, -2, 3, 11, 99, 100, 100000]
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>>> shuffle(array)
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>>> merge_sort(array)
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[-200, -10, -2, 3, 11, 99, 100, 100000]
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>>> array = [-200]
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>>> merge_sort(array)
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[-200]
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>>> array = [-2, 3, -10, 11, 99, 100000, 100, -200]
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>>> shuffle(array)
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>>> sorted(array) == merge_sort(array)
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True
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>>> array = [-2]
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>>> merge_sort(array)
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[-2]
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>>> array = []
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>>> merge_sort(array)
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[]
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>>> array = [10000000, 1, -1111111111, 101111111112, 9000002]
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>>> sorted(array) == merge_sort(array)
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True
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"""
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if len(array) <= 1:
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return array
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# the actual formula to calculate the middle element = left + (right - left) // 2
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# this avoids integer overflow in case of large N
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middle = 0 + (len(array) - 0) // 2
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# Split the array into halves till the array length becomes equal to One
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# merge the arrays of single length returned by mergeSort function and
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# pass them into the merge arrays function which merges the array
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left_half = array[:middle]
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right_half = array[middle:]
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return merge(merge_sort(left_half), merge_sort(right_half))
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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