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74 lines
2.2 KiB
Python
74 lines
2.2 KiB
Python
"""
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This is pure Python implementation of counting sort algorithm
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For doctests run following command:
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python -m doctest -v counting_sort.py
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or
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python3 -m doctest -v counting_sort.py
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For manual testing run:
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python counting_sort.py
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"""
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def counting_sort(collection):
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"""Pure implementation of counting sort algorithm in Python
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:param collection: some mutable ordered collection with heterogeneous
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comparable items inside
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:return: the same collection ordered by ascending
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Examples:
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>>> counting_sort([0, 5, 3, 2, 2])
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[0, 2, 2, 3, 5]
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>>> counting_sort([])
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[]
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>>> counting_sort([-2, -5, -45])
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[-45, -5, -2]
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"""
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# if the collection is empty, returns empty
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if collection == []:
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return []
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# get some information about the collection
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coll_len = len(collection)
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coll_max = max(collection)
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coll_min = min(collection)
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# create the counting array
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counting_arr_length = coll_max + 1 - coll_min
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counting_arr = [0] * counting_arr_length
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# count how much a number appears in the collection
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for number in collection:
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counting_arr[number - coll_min] += 1
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# sum each position with it's predecessors. now, counting_arr[i] tells
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# us how many elements <= i has in the collection
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for i in range(1, counting_arr_length):
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counting_arr[i] = counting_arr[i] + counting_arr[i - 1]
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# create the output collection
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ordered = [0] * coll_len
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# place the elements in the output, respecting the original order (stable
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# sort) from end to begin, updating counting_arr
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for i in reversed(range(coll_len)):
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ordered[counting_arr[collection[i] - coll_min] - 1] = collection[i]
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counting_arr[collection[i] - coll_min] -= 1
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return ordered
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def counting_sort_string(string):
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"""
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>>> counting_sort_string("thisisthestring")
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'eghhiiinrsssttt'
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"""
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return "".join([chr(i) for i in counting_sort([ord(c) for c in string])])
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if __name__ == "__main__":
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# Test string sort
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assert counting_sort_string("thisisthestring") == "eghhiiinrsssttt"
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user_input = input("Enter numbers separated by a comma:\n").strip()
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unsorted = [int(item) for item in user_input.split(",")]
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print(counting_sort(unsorted))
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