Radix sort

radix_sort.py

@@ -0,0 +1,63 @@
+"""This module contains the radix sort method (radix_srt), which performs an
+in-place sort on a passed in list. Radix sort has a best case time
+complexity of O(n log n). This implementation of radix sort is stable, but not
+adaptive.
+
+References:
+
+Radix Sort in Python
+http://www.geekviewpoint.com/python/sorting/radixsort
+by Isai Damier
+"""
+
+
+def radix_srt(un_list):
+    """Sort a list in place with radix sort.
+
+    args:
+        un_list: the list of positive integers to be sorted.
+    """
+    radix = 10
+    maxLen = False
+    tmp, placement = -1, 1
+
+    while not maxLen:
+        maxLen = True
+        buckets = [list() for num in range(radix)]
+
+        for i in un_list:
+            tmp = i // placement
+            buckets[tmp % radix].append(i)
+            if maxLen and tmp > 0:
+                maxLen = False
+
+        a = 0
+        for b in range(radix):
+            buck = buckets[b]
+            for i in buck:
+                un_list[a] = i
+                a += 1
+
+        placement *= radix
+
+
+if __name__ == '__main__':
+    from random import randint
+    WORST_CASE = [randint(9000, 10000) for x in range(1, 10001)]
+    BEST_CASE = [randint(0, 9) for x in range(1, 10001)]
+
+    from timeit import Timer
+
+    SETUP = """from __main__ import BEST_CASE, WORST_CASE, radix_srt"""
+
+    best = Timer('radix_srt({})'.format(BEST_CASE), SETUP).timeit(100)
+
+    worst = Timer('radix_srt({})'.format(WORST_CASE), SETUP).timeit(100)
+
+    print("""
+        Best case represented as a list with integers between 0 and 9.
+        Worst case represented as a list with large integers (here, between
+        9000 and 9999).
+        """)
+    print('Best Case: {}'.format(best))
+    print('Worst Case: {}'.format(worst))

test_radix_sort.py

@@ -0,0 +1,40 @@
+from random import shuffle
+import pytest
+
+from radix_sort import radix_srt
+
+
+def test_radix_srt():
+    expected = range(20)
+    actual = expected[:]
+    shuffle(actual)
+    radix_srt(actual)
+    assert expected == actual
+
+
+def test_radix_srt_with_duplicates():
+    expected = [1, 3, 3, 6, 7, 8, 8, 8]
+    actual = expected[:]
+    shuffle(actual)
+    radix_srt(actual)
+    assert expected == actual
+
+
+def test_radix_srt_with_zero_items():
+    expected = []
+    actual = []
+    radix_srt(actual)
+    assert expected == actual
+
+
+def test_radix_srt_with_one_item():
+    expected = [1]
+    actual = [1]
+    radix_srt(actual)
+    assert expected == actual
+
+
+def test_radix_sort_wrong_type():
+    with pytest.raises(TypeError):
+        radix_srt(15)
+