Merge pull request TheAlgorithms#19 from JakeBonek/master

Added Shell Sort

Author: harshildarji

README.md

@@ -73,6 +73,17 @@ __Properties__
 
 ###### View the algorithm in [action][selection-toptal]
 
+## Shell sort
+![alt text][shell-image]
+
+From [Wikipedia][shell-wiki]:  Shellsort is a generalization of insertion sort that allows the exchange of items that are far apart.  The idea is to arrange the list of elements so that, starting anywherem considereing every nth element gives a sorted list.  Such a list is said to be h-sorted.  Equivanelty, it can be thought of as h intterleaved lists, each individually sorted.
+
+__Properties__
+* Worst case performance O(nlog2 2n)
+* Best case performance O(n log n)
+* Average case performance depends on gap sequence
+
+###### View the algorithm in [action][shell-toptal]
 
 ## Search Algorithms
 
@@ -123,6 +134,11 @@ Mathematically a bijective function is used on the characters' positions to encr
 [selection-toptal]: https://www.toptal.com/developers/sorting-algorithms/selection-sort
 [selection-wiki]: https://en.wikipedia.org/wiki/Selection_sort
 [selection-image]: https://upload.wikimedia.org/wikipedia/commons/thumb/b/b0/Selection_sort_animation.gif/250px-Selection_sort_animation.gif "Selection Sort Sort"
+
+[shell-toptal]: https://www.toptal.com/developers/sorting-algorithms/shell-sort
+[shell-wiki]: https://en.wikipedia.org/wiki/Shellsort
+[shell-image]: https://upload.wikimedia.org/wikipedia/commons/d/d8/Sorting_shellsort_anim.gif "Shell Sort"
+
 [caesar]: https://upload.wikimedia.org/wikipedia/commons/4/4a/Caesar_cipher_left_shift_of_3.svg
 [linear-wiki]: https://en.wikipedia.org/wiki/Linear_search
 [linear-image]: http://www.tutorialspoint.com/data_structures_algorithms/images/linear_search.gif

sorts/bogosort.py

@@ -1,5 +1,5 @@
 """
-This is pure python implementation of bogosort algorithm
+This is a pure python implementation of the bogosort algorithm
 For doctests run following command:
 python -m doctest -v bogosort.py
 or
@@ -12,7 +12,7 @@
 import random
 
 def bogosort(collection):
-    """Pure implementation of bogosort algorithm in Python
+    """Pure implementation of the bogosort algorithm in Python
     :param collection: some mutable ordered collection with heterogeneous
     comparable items inside
     :return: the same collection ordered by ascending
@@ -47,6 +47,6 @@ def isSorted(collection):
     else:
         input_function = input
 
-    user_input = input_function('Enter numbers separated by coma:\n')
+    user_input = input_function('Enter numbers separated by a comma:\n')
     unsorted = [int(item) for item in user_input.split(',')]
     print(bogosort(unsorted))

sorts/bubble_sort.py

@@ -47,6 +47,6 @@ def bubble_sort(collection):
     else:
         input_function = input
 
-    user_input = input_function('Enter numbers separated by coma:\n')
+    user_input = input_function('Enter numbers separated by a comma:\n')
     unsorted = [int(item) for item in user_input.split(',')]
     print(bubble_sort(unsorted))

sorts/heap_sort.py

@@ -1,4 +1,14 @@
+"""
+This is a pure python implementation of the heap sort algorithm.
 
+For doctests run following command:
+python -m doctest -v heap_sort.py
+or
+python3 -m doctest -v heap_sort.py
+
+For manual testing run:
+python insertion_sort.py
+"""
 from  __future__ import print_function
 
 
@@ -17,13 +27,28 @@ def heapify(unsorted,index,heap_size):
 		heapify(unsorted,largest,heap_size)		
 
 def heap_sort(unsorted):	
-	n=len(unsorted) 
-	for i in range (n/2 - 1 , -1, -1) :
-		heapify(unsorted,i,n)
-	for i in range(n - 1,  -1, -1):
-		unsorted[0], unsorted[i] = unsorted[i], unsorted[0]
-		heapify(unsorted,0,i)
-	return unsorted
+    """Pure implementation of the heap sort algorithm in Python
+    :param collection: some mutable ordered collection with heterogeneous
+    comparable items inside
+    :return: the same collection ordered by ascending
+
+    Examples:
+    >>> heap_sort([0, 5, 3, 2, 2])
+    [0, 2, 2, 3, 5]
+
+    >>> heap_sort([])
+    []
+
+    >>> heap_sort([-2, -5, -45])
+    [-45, -5, -2]
+    """
+    n=len(unsorted)
+    for i in range (n/2 - 1 , -1, -1):
+	heapify(unsorted,i,n)
+    for i in range(n - 1,  -1, -1):
+	unsorted[0], unsorted[i] = unsorted[i], unsorted[0]
+	heapify(unsorted,0,i)
+    return unsorted
 
 
 if __name__ == '__main__':
@@ -33,7 +58,6 @@ def heap_sort(unsorted):
     else:
         input_function = input
 
-    user_input = input_function('Enter numbers separated by coma:\n')
+    user_input = input_function('Enter numbers separated by a comma:\n')
     unsorted = [int(item) for item in user_input.split(',')]
     print (heap_sort(unsorted))
-

sorts/insertion_sort.py

@@ -1,5 +1,5 @@
 """
-This is pure python implementation of insertion sort algorithm
+This is a pure python implementation of the insertion sort algorithm
 
 For doctests run following command:
 python -m doctest -v insertion_sort.py
@@ -13,7 +13,7 @@
 
 
 def insertion_sort(collection):
-    """Pure implementation of insertion sort algorithm in Python
+    """Pure implementation of the insertion sort algorithm in Python
 
     :param collection: some mutable ordered collection with heterogeneous
     comparable items inside
@@ -51,6 +51,6 @@ def insertion_sort(collection):
     else:
         input_function = input
 
-    user_input = input_function('Enter numbers separated by coma:\n')
+    user_input = input_function('Enter numbers separated by a comma:\n')
     unsorted = [int(item) for item in user_input.split(',')]
     print(insertion_sort(unsorted))

sorts/merge_sort.py

@@ -1,5 +1,5 @@
 """
-This is pure python implementation of merge sort algorithm
+This is a pure python implementation of the merge sort algorithm
 
 For doctests run following command:
 python -m doctest -v merge_sort.py
@@ -13,7 +13,7 @@
 
 
 def merge_sort(collection):
-    """Pure implementation of merge sort algorithm in Python
+    """Pure implementation of the merge sort algorithm in Python
 
     :param collection: some mutable ordered collection with heterogeneous
     comparable items inside
@@ -71,6 +71,6 @@ def merge_sort(collection):
     else:
         input_function = input
 
-    user_input = input_function('Enter numbers separated by coma:\n')
+    user_input = input_function('Enter numbers separated by a comma:\n')
     unsorted = [int(item) for item in user_input.split(',')]
     print(merge_sort(unsorted))

sorts/quick_sort.py

@@ -1,5 +1,5 @@
 """
-This is pure python implementation of quick sort algorithm
+This is a pure python implementation of the quick sort algorithm
 
 For doctests run following command:
 python -m doctest -v quick_sort.py
@@ -62,6 +62,6 @@ def quick_sort(collection):
     else:
         input_function = input
 
-    user_input = input_function('Enter numbers separated by coma:\n')
+    user_input = input_function('Enter numbers separated by a comma:\n')
     unsorted = [int(item) for item in user_input.split(',')]
     print(sort(unsorted))

sorts/selection_sort.py

@@ -1,5 +1,5 @@
 """
-This is pure python implementation of selection sort algorithm
+This is a pure python implementation of the selection sort algorithm
 
 For doctests run following command:
 python -m doctest -v selection_sort.py
@@ -13,7 +13,11 @@
 
 
 def selection_sort(collection):
-    """Pure implementation of selection sort algorithm in Python
+    """Pure implementation of the selection sort algorithm in Python
+    :param collection: some mutable ordered collection with heterogeneous
+    comparable items inside
+    :return: the same collection ordered by ascending
+    
 
     Examples:
     >>> selection_sort([0, 5, 3, 2, 2])
@@ -24,11 +28,8 @@ def selection_sort(collection):
 
     >>> selection_sort([-2, -5, -45])
     [-45, -5, -2]
-
-    :param collection: some mutable ordered collection with heterogeneous
-    comparable items inside
-    :return: the same collection ordered by ascending
     """
+   
     length = len(collection)
     for i in range(length):
         least = i
@@ -50,6 +51,6 @@ def selection_sort(collection):
     else:
         input_function = input
 
-    user_input = input_function('Enter numbers separated by coma:\n')
+    user_input = input_function('Enter numbers separated by a comma:\n')
     unsorted = [int(item) for item in user_input.split(',')]
     print(selection_sort(unsorted))

sorts/shell_sort.py

@@ -0,0 +1,58 @@
+"""
+This is a pure python implementation of the shell sort algorithm
+
+For doctests run following command:
+python -m doctest -v shell_sort.py
+or
+python3 -m doctest -v shell_sort.py
+
+For manual testing run:
+python shell_sort.py
+"""
+from __future__ import print_function
+
+
+def shell_sort(collection):
+    """Pure implementation of shell sort algorithm in Python
+    :param collection:  Some mutable ordered collection with heterogeneous
+    comparable items inside
+    :return:  the same collection ordered by ascending
+    
+    >>> shell_sort([0, 5, 3, 2, 2)]
+    [0, 2, 2, 3, 5]
+
+    >>> shell_sort([])
+    []
+     
+    >>> shell_sort([-2, -5, -45]) 
+    [-45, -5, -2]
+    """
+    # Marcin Ciura's gap sequence
+    gaps = [701, 301, 132, 57, 23, 10, 4, 1]
+    
+    for gap in gaps:
+        i = gap
+        while i < len(collection):
+            temp = collection[i]
+            j = i
+            while j >= gap and collection[j-gap] > temp:
+                collection[j] = collection[j - gap]
+                j -= gap
+            collection[j] = temp
+            i += 1
+        
+        
+    return collection
+
+if __name__ == '__main__':
+    import sys
+    # For python 2.x and 3.x compatibility: 3.x has not 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(shell_sort(unsorted))