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73 lines
2.2 KiB
Python
73 lines
2.2 KiB
Python
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"""
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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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from __future__ import print_function
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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(0, 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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if __name__ == '__main__':
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import sys
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# For python 2.x and 3.x compatibility: 3.x has not raw_input builtin
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# otherwise 2.x's input builtin function is too "smart"
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if sys.version_info.major < 3:
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input_function = raw_input
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else:
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input_function = input
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user_input = input_function('Enter numbers separated by a comma:\n')
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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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