Python/sorts/counting_sort.py

74 lines
2.2 KiB
Python
Raw Normal View History

2017-10-14 03:07:02 +00:00
"""
This is pure Python implementation of counting sort algorithm
2017-10-14 03:07:02 +00:00
For doctests run following command:
python -m doctest -v counting_sort.py
or
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):
2019-10-05 05:14:13 +00:00
counting_arr[i] = counting_arr[i] + counting_arr[i - 1]
2017-10-14 03:07:02 +00:00
# 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)):
2019-10-05 05:14:13 +00:00
ordered[counting_arr[collection[i] - coll_min] - 1] = collection[i]
2017-10-14 03:07:02 +00:00
counting_arr[collection[i] - coll_min] -= 1
return ordered
2019-10-05 05:14:13 +00:00
2018-10-02 09:36:24 +00:00
def counting_sort_string(string):
"""
>>> counting_sort_string("thisisthestring")
'eghhiiinrsssttt'
"""
2019-10-05 05:14:13 +00:00
return "".join([chr(i) for i in counting_sort([ord(c) for c in string])])
2018-10-02 09:36:24 +00:00
2017-10-14 03:07:02 +00:00
2019-10-05 05:14:13 +00:00
if __name__ == "__main__":
2018-10-02 09:36:24 +00:00
# Test string sort
assert counting_sort_string("thisisthestring") == "eghhiiinrsssttt"
2018-10-02 09:36:24 +00:00
2019-10-05 05:14:13 +00:00
user_input = input("Enter numbers separated by a comma:\n").strip()
unsorted = [int(item) for item in user_input.split(",")]
2017-10-14 03:07:02 +00:00
print(counting_sort(unsorted))