data_structures/linked_list: Add __len__() function and tests (#2047)

* Update __init__.py

please add a function to get length of linked list

* Update __init__.py

* Update doubly_linked_list.py

all size function lo doubly linked list class

* prime number _better method

* comments

* Updated init.py 2

made it more pythonic

* updated length function

* commnet in linked_list construtor

* Update data_structures/linked_list/__init__.py

accepecting changes

Co-authored-by: Christian Clauss <[email protected]>

* Update data_structures/linked_list/__init__.py

Co-authored-by: Christian Clauss <[email protected]>

* Update __init__.py

* Revert changes to doubly_linked_list.py

* Revert changes to prime_check.py

Co-authored-by: Christian Clauss <[email protected]>

Author: Lakshmikanth2001

Diff for: data_structures/linked_list/__init__.py

@@ -7,17 +7,40 @@ def __init__(self, item, next):
 class LinkedList:
     def __init__(self):
         self.head = None
+        self.size = 0
 
     def add(self, item):
         self.head = Node(item, self.head)
+        self.size += 1
 
     def remove(self):
         if self.is_empty():
             return None
         else:
             item = self.head.item
             self.head = self.head.next
+            self.size -= 1
             return item
 
     def is_empty(self):
         return self.head is None
+
+    def __len__(self):
+        """
+        >>> linked_list = LinkedList()
+        >>> len(linked_list)
+        0
+        >>> linked_list.add("a")
+        >>> len(linked_list)
+        1
+        >>> linked_list.add("b")
+        >>> len(linked_list)
+        2
+        >>> _ = linked_list.remove()
+        >>> len(linked_list)
+        1
+        >>> _ = linked_list.remove()
+        >>> len(linked_list)
+        0
+        """
+        return self.size