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65 lines
2.1 KiB
Python
65 lines
2.1 KiB
Python
"""A merge sort which accepts an array as input and recursively
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splits an array in half and sorts and combines them.
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"""
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"""https://en.wikipedia.org/wiki/Merge_sort """
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def merge(arr: list[int]) -> list[int]:
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"""Return a sorted array.
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>>> merge([10,9,8,7,6,5,4,3,2,1])
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[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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>>> merge([1,2,3,4,5,6,7,8,9,10])
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[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
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>>> merge([10,22,1,2,3,9,15,23])
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[1, 2, 3, 9, 10, 15, 22, 23]
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>>> merge([100])
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[100]
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>>> merge([])
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[]
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"""
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if len(arr) > 1:
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middle_length = len(arr) // 2 # Finds the middle of the array
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left_array = arr[
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:middle_length
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] # Creates an array of the elements in the first half.
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right_array = arr[
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middle_length:
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] # Creates an array of the elements in the second half.
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left_size = len(left_array)
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right_size = len(right_array)
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merge(left_array) # Starts sorting the left.
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merge(right_array) # Starts sorting the right
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left_index = 0 # Left Counter
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right_index = 0 # Right Counter
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index = 0 # Position Counter
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while (
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left_index < left_size and right_index < right_size
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): # Runs until the lowers size of the left and right are sorted.
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if left_array[left_index] < right_array[right_index]:
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arr[index] = left_array[left_index]
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left_index += 1
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else:
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arr[index] = right_array[right_index]
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right_index += 1
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index += 1
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while (
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left_index < left_size
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): # Adds the left over elements in the left half of the array
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arr[index] = left_array[left_index]
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left_index += 1
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index += 1
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while (
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right_index < right_size
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): # Adds the left over elements in the right half of the array
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arr[index] = right_array[right_index]
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right_index += 1
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index += 1
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return arr
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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