Add counting sort (#35)

Add counting sort with test

docs/source/sorting.rst

@@ -38,4 +38,9 @@ Quick Sort
 Sleep Sort
 ----------
 
-.. autofunction:: pydsa.sleep_sort
+.. autofunction:: pydsa.sleep_sort
+
+Counting Sort
+----------
+
+.. autofunction:: pydsa.counting_sort

pydsa/__init__.py

@@ -9,3 +9,4 @@
 from .binary_search import binary_search
 from .linear_search import linear_search
 from .queue import queue
+from .counting_sort import counting_sort

pydsa/counting_sort.py

@@ -0,0 +1,24 @@
+# Counting Sort
+# Complexity : O(n + (range of input))
+# https://en.wikibooks.org/wiki/Algorithm_Implementation/Sorting/Counting_sort
+
+
+def counting_sort(array, maxval):
+    """
+    Sorts the list 'array' using counting sort
+
+    >>> from pydsa import counting_sort
+    >>> a = [5, 6, 1, 9, 3]
+    >>> counting_sort(a, 9)
+    [1, 3, 5, 6, 9]
+
+    """
+    count = [0] * (maxval + 1)
+    for a in array:
+        count[a] += 1
+    i = 0
+    for a in range(maxval + 1):
+        for c in range(count[a]):
+            array[i] = a
+            i += 1
+    return array

pydsa/tests/test_counting_sort.py

@@ -0,0 +1,7 @@
+from pydsa.counting_sort import counting_sort
+from random import randint
+
+
+def test_counting_sort():
+    a = b = [randint(1, 100) for i in range(100)]
+    assert counting_sort(a, max(a)) == sorted(b)