Added Shell Sort in Python

Python/Algorithms/Sorting-Algorithms/shell_sort.py

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+# Python program for implementation of Shell Sort
+
+# Shell sort is an algorithm that first sorts the elements far apart
+# from each other and successively reduces the interval 
+# between the elements to be sorted. It is a generalized version of insertion sort.'''
+
+def shellSort(values): 
+
+ # Start with a somewhat big gap, then reduce the gap
+ n = len(values)
+ gap = n//2
+
+ # Do a gapped insertion sort for this gap size.
+ # The first gap elements are already in gapped
+ # order keep adding one more element until the entire array
+ # is gap sorted
+ while gap > 0: 
+
+ for i in range(gap,n): 
+
+ # add a[i] to the elements that have been gap sorted
+ # save a[i] in temp and make a hole at position i
+ temp = values[i]
+
+ # shift earlier gap-sorted elements up until the correct
+ # location if a[i] is found
+ j = i
+ while j >= gap and values[j-gap] >temp:
+ values[j] = values[j-gap]
+ j -= gap
+
+ # put temporary variable in its correct location
+ values[j] = temp
+ gap //= 2
+
+
+# Insert Test Values
+values = [1, 2, 4, 12, 34, 54, 2, 3, 9, 15, 20]
+n = len(values)
+
+print ("Array before sorting: "+ str(values))
+
+shellSort(values)
+
+print ("Array after sorting:"+ str(values))
+