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"""

This is pure Python implementation of counting sort algorithm

For doctests run following command:

python -m doctest -v counting_sort.py

python3 -m doctest -v counting_sort.py

For manual testing run:

python counting_sort.py

"""

def counting_sort(collection):

"""Pure implementation of counting sort algorithm in Python

:param collection: some mutable ordered collection with heterogeneous

comparable items inside

:return: the same collection ordered by ascending

Examples:

>>> counting_sort([0, 5, 3, 2, 2])

[0, 2, 2, 3, 5]

>>> counting_sort([])

[]

>>> counting_sort([-2, -5, -45])

[-45, -5, -2]

"""

# if the collection is empty, returns empty

if collection == []:

return []

# get some information about the collection

coll_len = len(collection)

coll_max = max(collection)

coll_min = min(collection)

# create the counting array

counting_arr_length = coll_max + 1 - coll_min

counting_arr = [0] * counting_arr_length

# count how much a number appears in the collection

for number in collection:

counting_arr[number - coll_min] += 1

# sum each position with it's predecessors. now, counting_arr[i] tells

# us how many elements <= i has in the collection

for i in range(1, counting_arr_length):

counting_arr[i] = counting_arr[i] + counting_arr[i - 1]

# create the output collection

ordered = [0] * coll_len

# place the elements in the output, respecting the original order (stable

# sort) from end to begin, updating counting_arr

for i in reversed(range(0, coll_len)):

ordered[counting_arr[collection[i] - coll_min] - 1] = collection[i]

counting_arr[collection[i] - coll_min] -= 1

return ordered

def counting_sort_string(string):

"""

>>> counting_sort_string("thisisthestring")

'eghhiiinrsssttt'

"""

return "".join([chr(i) for i in counting_sort([ord(c) for c in string])])

if __name__ == "__main__":

# Test string sort

assert "eghhiiinrsssttt" == counting_sort_string("thisisthestring")

user_input = input("Enter numbers separated by a comma:\n").strip()

unsorted = [int(item) for item in user_input.split(",")]

print(counting_sort(unsorted))

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