added counting sort

sorts/counting_sort.py

@@ -0,0 +1,57 @@
+"""
+This is pure python implementation of counting sort algorithm
+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
+"""
+
+from __future__ import print_function
+
+
+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]
+    """
+    length = len(collection)
+    maximum = max(collection)
+    minimum = min(collection)
+    counting_arr_length = maximum + 1 + abs(minimum)
+    counting_arr = [0] * counting_arr_length
+    for i in range(counting_arr_length):
+        for j in range(length):
+            if collection[j] == i + minimum:
+                counting_arr[i] += 1
+
+    j = 0
+    for i in range(counting_arr_length):
+        for k in range(counting_arr[i]):
+            collection[j] = i + minimum
+            j += 1
+
+    return collection
+
+
+if __name__ == '__main__':
+    import sys
+    # For python 2.x and 3.x compatibility: 3.x has not raw_input builtin
+    # otherwise 2.x's input builtin function is too "smart"
+    if sys.version_info.major < 3:
+        input_function = raw_input
+    else:
+        input_function = input
+
+    user_input = input_function('Enter numbers separated by a comma:\n')
+    unsorted = [int(item) for item in user_input.split(',')]
+print(counting_sort(unsorted))