Optimization shell sort (#4119)

* optimization

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: realDuYuanChao

sorts/shell_sort.py

@@ -26,7 +26,8 @@ def shell_sort(collection):
             while j >= gap and collection[j - gap] > insert_value:
                 collection[j] = collection[j - gap]
                 j -= gap
-            collection[j] = insert_value
+            if j != i:
+                collection[j] = insert_value
     return collection