Update 4.shellSort.md

Author: JerryChii

4.shellSort.md

@@ -63,6 +63,30 @@ def shellSort(arr):
 }
 ```
 
+不太明白作者一下代码的含义，
+```python
+while(gap < len(arr)/3):
+    gap = gap*3+1
+```
+按照大部分博客说每次都除以2，以下代码也是可行的
+```python
+def shellSort(arr):
+    import math
+    gap=len(arr)/2
+    
+    while gap > 0:
+        for i in range(gap,len(arr)):
+            temp = arr[i]
+            j = i-gap
+            while j >=0 and arr[j] > temp:
+                arr[j+gap]=arr[j]
+                j-=gap
+            arr[j+gap] = temp
+        gap = gap/2
+    return arr
+
+```
+
 ## 4. Go 代码实现
 
 ```go