Adds operations for circular linked list (#1584)

* Adds, append, len, print operations for circular linked list

* Adds, prepend support

* Adds, delete from front of the list

* Adds, delete_rear support

* Adds, method documentations

* Adds, type checking and doctests

* Updates doctest for delete ops

* Addressing requested changes

* Removes unused import

* Fixes failing doctests

* Minor modifications...

data_structures/linked_list/circular_linked_list.py

@@ -0,0 +1,186 @@
+from typing import Any
+
+
+class Node:
+    """
+    Class to represent a single node.
+
+    Each node has following attributes
+    * data
+    * next_ptr
+    """
+
+    def __init__(self, data: Any):
+        self.data = data
+        self.next_ptr = None
+
+
+class CircularLinkedList:
+    """
+    Class to represent the CircularLinkedList.
+
+    CircularLinkedList has following attributes.
+    * head
+    * length
+    """
+
+    def __init__(self):
+        self.head = None
+        self.length = 0
+
+    def __len__(self) -> int:
+        """
+        Dunder method to return length of the CircularLinkedList
+        >>> cll = CircularLinkedList()
+        >>> len(cll)
+        0
+        >>> cll.append(1)
+        >>> len(cll)
+        1
+        """
+        return self.length
+
+    def __str__(self) -> str:
+        """
+        Dunder method to represent the string representation of the CircularLinkedList
+        >>> cll = CircularLinkedList()
+        >>> print(cll)
+        Empty linked list
+        >>> cll.append(1)
+        >>> cll.append(2)
+        >>> print(cll)
+        <Node data=1> => <Node data=2>
+        """
+        current_node = self.head
+        if not current_node:
+            return "Empty linked list"
+
+        results = [current_node.data]
+        current_node = current_node.next_ptr
+
+        while current_node != self.head:
+            results.append(current_node.data)
+            current_node = current_node.next_ptr
+
+        return " => ".join(f"<Node data={result}>" for result in results)
+
+    def append(self, data: Any) -> None:
+        """
+        Adds a node with given data to the end of the CircularLinkedList
+        >>> cll = CircularLinkedList()
+        >>> cll.append(1)
+        >>> print(f"{len(cll)}: {cll}")
+        1: <Node data=1>
+        >>> cll.append(2)
+        >>> print(f"{len(cll)}: {cll}")
+        2: <Node data=1> => <Node data=2>
+        """
+        current_node = self.head
+
+        new_node = Node(data)
+        new_node.next_ptr = new_node
+
+        if current_node:
+            while current_node.next_ptr != self.head:
+                current_node = current_node.next_ptr
+
+            current_node.next_ptr = new_node
+            new_node.next_ptr = self.head
+        else:
+            self.head = new_node
+
+        self.length += 1
+
+    def prepend(self, data: Any) -> None:
+        """
+        Adds a ndoe with given data to the front of the CircularLinkedList
+        >>> cll = CircularLinkedList()
+        >>> cll.prepend(1)
+        >>> cll.prepend(2)
+        >>> print(f"{len(cll)}: {cll}")
+        2: <Node data=2> => <Node data=1>
+        """
+        current_node = self.head
+
+        new_node = Node(data)
+        new_node.next_ptr = new_node
+
+        if current_node:
+            while current_node.next_ptr != self.head:
+                current_node = current_node.next_ptr
+
+            current_node.next_ptr = new_node
+            new_node.next_ptr = self.head
+
+        self.head = new_node
+        self.length += 1
+
+    def delete_front(self) -> None:
+        """
+        Removes the 1st node from the CircularLinkedList
+        >>> cll = CircularLinkedList()
+        >>> cll.delete_front()
+        Traceback (most recent call last):
+        ...
+        IndexError: Deleting from an empty list
+        >>> cll.append(1)
+        >>> cll.append(2)
+        >>> print(f"{len(cll)}: {cll}")
+        2: <Node data=1> => <Node data=2>
+        >>> cll.delete_front()
+        >>> print(f"{len(cll)}: {cll}")
+        1: <Node data=2>
+        """
+        if not self.head:
+            raise IndexError("Deleting from an empty list")
+
+        current_node = self.head
+
+        if current_node.next_ptr == current_node:
+            self.head, self.length = None, 0
+        else:
+            while current_node.next_ptr != self.head:
+                current_node = current_node.next_ptr
+
+            current_node.next_ptr = self.head.next_ptr
+            self.head = self.head.next_ptr
+
+        self.length -= 1
+
+    def delete_rear(self) -> None:
+        """
+        Removes the last node from the CircularLinkedList
+        >>> cll = CircularLinkedList()
+        >>> cll.delete_rear()
+        Traceback (most recent call last):
+        ...
+        IndexError: Deleting from an empty list
+        >>> cll.append(1)
+        >>> cll.append(2)
+        >>> print(f"{len(cll)}: {cll}")
+        2: <Node data=1> => <Node data=2>
+        >>> cll.delete_rear()
+        >>> print(f"{len(cll)}: {cll}")
+        1: <Node data=1>
+        """
+        if not self.head:
+            raise IndexError("Deleting from an empty list")
+
+        temp_node, current_node = self.head, self.head
+
+        if current_node.next_ptr == current_node:
+            self.head, self.length = None, 0
+        else:
+            while current_node.next_ptr != self.head:
+                temp_node = current_node
+                current_node = current_node.next_ptr
+
+            temp_node.next_ptr = current_node.next_ptr
+
+        self.length -= 1
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()