Added Dequeue in Python

sorts/merge_sort.py

@@ -0,0 +1,76 @@
+"""
+This is a pure python implementation of the merge sort algorithm
+
+For doctests run following command:
+python -m doctest -v merge_sort.py
+or
+python3 -m doctest -v merge_sort.py
+
+For manual testing run:
+python merge_sort.py
+"""
+from __future__ import print_function
+
+
+def merge_sort(collection):
+    """Pure implementation of the merge sort algorithm in Python
+
+    :param collection: some mutable ordered collection with heterogeneous
+    comparable items inside
+    :return: the same collection ordered by ascending
+
+    Examples:
+    >>> merge_sort([0, 5, 3, 2, 2])
+    [0, 2, 2, 3, 5]
+
+    >>> merge_sort([])
+    []
+
+    >>> merge_sort([-2, -5, -45])
+    [-45, -5, -2]
+    """
+    length = len(collection)
+    if length > 1:
+        midpoint = length // 2
+        left_half = merge_sort(collection[:midpoint])
+        right_half = merge_sort(collection[midpoint:])
+        i = 0
+        j = 0
+        k = 0
+        left_length = len(left_half)
+        right_length = len(right_half)
+        while i < left_length and j < right_length:
+            if left_half[i] < right_half[j]:
+                collection[k] = left_half[i]
+                i += 1
+            else:
+                collection[k] = right_half[j]
+                j += 1
+            k += 1
+
+        while i < left_length:
+            collection[k] = left_half[i]
+            i += 1
+            k += 1
+
+        while j < right_length:
+            collection[k] = right_half[j]
+            j += 1
+            k += 1
+
+    return collection
+
+
+if __name__ == '__main__':
+    import sys
+
+    # For python 2.x and 3.x compatibility: 3.x has no 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(merge_sort(unsorted))