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What is a circular linked list (circular linked list)?

Data StructuresJunior~2 min read
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A circular linked list is a variation of a linked list in which the last node does not point to None, but instead references back to the first node (head), forming a closed loop.

That is, during traversal you can move endlessly in a circle: after the last element comes the first one again.

1. Visually

Singly linked circular list:

javascript
head → [10 | *] → [20 | *] → [30 | *] ──┐ ↑──────────────────────────────┘
  • The last node's next points to head.
  • There is no "end of the list": traversal can start from any node and will always come back around.

2. Doubly linked circular list

Here, each node has both prev and next, and both pointers close into a loop:

javascript
↰ [10] ↔ [20] ↔ [30] ↺
  • head.prev = tail
  • tail.next = head

3. How it is stored

Each node has references like in a regular list, but:

  • when the last element is created, its next points to head,
  • (in the doubly linked variant, head.prev also points to tail).

4. Basic operations

OperationComplexityDescription
TraversalO(n)You can traverse starting from any node, but you need to watch out for looping forever.
Insertion/deletion given a known nodeO(1)References are simply reassigned.
SearchO(n)Same as in a regular list.

5. Advantages

  • You can traverse the list in a circle without checking for an "end."
  • Convenient for circular structures: queues, buffers, game loops, round-robin task distribution.
  • There is no "dead end" (None); every node is connected to others.

6. Disadvantages

  • You need to work carefully with the loop, otherwise the program can get stuck in endless traversal.
  • Harder to control the beginning and the end.

7. Example in Python

python
class Node: def __init__(self, data): self.data = data self.next = None # creating a circular list: 10 → 20 → 30 → back to 10 n1 = Node(10) n2 = Node(20) n3 = Node(30) n1.next = n2 n2.next = n3 n3.next = n1 # loop head = n1

Summary:

A circular linked list is a linked list in which the last element references back to the first one. Such a structure forms a ring, convenient for implementing circular queues, buffers, and repeating processes.

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