Added merge sort

Author: OmkarPathak

pygorithms/sorting/merge_sort.py

@@ -0,0 +1,47 @@
+# Author: OMKAR PATHAK
+# Created On: 31st July 2017
+
+# Best = Average = Worst = O(nlog(n))
+
+# merge function to merge the separated lists
+def merge(a,b):
+    """ Function to merge two arrays """
+    c = []
+    while len(a) != 0 and len(b) != 0:
+        if a[0] < b[0]:
+            c.append(a[0])
+            a.remove(a[0])
+        else:
+            c.append(b[0])
+            b.remove(b[0])
+    if len(a) == 0:
+        c += b
+    else:
+        c += a
+    return c
+
+# Code for merge sort
+def sort(x):
+    """ Function to sort an array using merge sort algorithm """
+    if len(x) == 0 or len(x) == 1:
+        return x
+    else:
+        middle = len(x)//2
+        a = sort(x[:middle])
+        b = sort(x[middle:])
+        return merge(a,b)
+
+# time complexities
+def bestcase_complexity():
+    return 'O(nlogn)'
+
+def averagecase_complexity():
+    return 'O(nlogn)'
+
+def worstcase_complexity():
+    return 'O(nlogn)'
+
+# easily retrieve the source code of the sort function
+def get_code():
+    import inspect
+    return inspect.getsource(sort), inspect.getsource(merge)