added shell sort (abranhe#27)

abranhe · web-flow · commit 4b313f1aa841 · 2019-10-02T14:08:55.000-04:00
added shell sort
diff --git a/allalgorithms/sorting/shell_sort.py b/allalgorithms/sorting/shell_sort.py
@@ -0,0 +1,30 @@
+# -*- coding: UTF-8 -*-
+#
+# Shell Sort Algorithm
+# The All ▲lgorithms library for python
+#
+# Contributed by: Elias
+# Github: @eliasbayona
+#
+
+def shell_sort(arr): 
+    n = len(arr) 
+    h = int(n/2)
+
+
+    while h > 0: 
+        for i in range(h,n):
+            
+            temp = arr[i] 
+            j = i 
+
+            while  j >= h and arr[j-h] >temp: 
+                arr[j] = arr[j-h] 
+                j -= h 
+
+            arr[j] = temp 
+
+        h = int(h/2)
+        
+    return arr
+
diff --git a/docs/sorting/shell-sort.md b/docs/sorting/shell-sort.md
@@ -0,0 +1,29 @@
+# Selection Sort
+
+In computer science, shell sort improves upon insertion sort by moving out of order elements more than one position at a time. It has a best case O(n log n) time complexity, and for other cases, it depends on the gap sequence. According to Poonen Theorem, worst case complexity for shell sort is Θ(NlogN)^2/(log logN)^2) or Θ(NlogN)^2/log logN) or Θ(N(logN)^2) or something in between.
+## Install
+
+```
+pip install allalgorithms
+```
+
+## Usage
+
+```py
+from allalgorithms.sorting import shell_sort
+
+arr = [77, 2, 10, -2, 1, 7]
+
+print(shell_sort(arr))
+# -> [-2, 1, 2, 7, 10, 77]
+```
+
+## API
+
+### selection_sort(array)
+
+> Returns a sorted array
+
+##### Params:
+
+- `array`: Unsorted Array
diff --git a/tests/test_sorting.py b/tests/test_sorting.py
@@ -8,7 +8,8 @@
     pigeonhole_sort,
     stooge_sort,
     cocktail_shaker_sort,
-    tree_sort
+    tree_sort,
+    shell_sort,
 )
 
 
@@ -37,6 +38,8 @@ def test_cocktail_shaker_sort(self):
     def tree_sort(self):
         self.assertEqual([-44, 1, 2, 3, 7, 19], tree_sort([7, 3, 2, 19, -44, 1]))
 
+    def test_shell_sort(self):
+        self.assertEqual([-44, 1, 2, 3, 7, 19], shell_sort([7, 3, 2, 19, -44, 1]))
 
 if __name__ == "__main__":
     unittest.main()
