Circular Linked List in Data Structures – Operations, Examples & Code

Circular Linked List

🚀 Introduction

A Circular Linked List is a type of linked list where:

👉 The last node points back to the first node (head) instead of NULL.

This creates a loop (circle) in the list.

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🔹 Structure

10 → 20 → 30 → 40
↑               ↓
←←←←←←←←←←←←←←←

👉 No NULL pointer in circular linked list.

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🔹 Key Characteristics

• Last node connects to head
• Traversal can start from any node
• No NULL at the end

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🔹 Operations in Circular Linked List

1. Traversal
2. Insertion
3. Deletion

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🔹 1. Traversal

💡 Concept

• Start from head
• Stop when you reach head again

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🧑‍💻 Example

public function traverse() {
    if ($this->head == null) return;    $temp = $this->head;    do {
        echo $temp->data . " → ";
        $temp = $temp->next;
    } while ($temp != $this->head);    echo "(back to head)";
}

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⚡ Complexity

👉 O(n)

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🔹 2. Insertion

✅ Insert at Beginning

💡 Concept

• Insert new node before head
• Update last node’s next to new node

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🧑‍💻 Code

public function insertAtBeginning($data) {
    $newNode = new Node($data);    if ($this->head == null) {
        $this->head = $newNode;
        $newNode->next = $this->head;
        return;
    }    $temp = $this->head;    while ($temp->next != $this->head) {
        $temp = $temp->next;
    }    $newNode->next = $this->head;
    $temp->next = $newNode;
    $this->head = $newNode;
}

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✅ Insert at End

💡 Concept

• Traverse to last node
• Insert new node and link to head

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🧑‍💻 Code

public function insertAtEnd($data) {
    $newNode = new Node($data);    if ($this->head == null) {
        $this->head = $newNode;
        $newNode->next = $this->head;
        return;
    }    $temp = $this->head;    while ($temp->next != $this->head) {
        $temp = $temp->next;
    }    $temp->next = $newNode;
    $newNode->next = $this->head;
}

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🔹 3. Deletion

✅ Delete from Beginning

public function deleteFromBeginning() {
    if ($this->head == null) return;    if ($this->head->next == $this->head) {
        $this->head = null;
        return;
    }    $temp = $this->head;    while ($temp->next != $this->head) {
        $temp = $temp->next;
    }    $this->head = $this->head->next;
    $temp->next = $this->head;
}

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✅ Delete from End

public function deleteFromEnd() {
    if ($this->head == null) return;    if ($this->head->next == $this->head) {
        $this->head = null;
        return;
    }    $temp = $this->head;    while ($temp->next->next != $this->head) {
        $temp = $temp->next;
    }    $temp->next = $this->head;
}

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⚡ Time Complexity

Operation	Complexity
Traversal	O(n)
Insertion	O(n)
Deletion	O(n)

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🎯 Advantages

✅ No NULL pointers
✅ Efficient for circular applications
✅ Any node can be starting point

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❌ Disadvantages

❌ Infinite loop risk
❌ More complex than singly linked list

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🧠 Real-World Use Cases

• Music playlist (looping songs)
• Round-robin scheduling
• Multiplayer games turn system

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🧠 Interview Tips

👉 Common questions:

• Detect circular linked list
• Split circular list
• Josephus problem

👉 Always remember:
👉 Use do-while loop instead of while loop

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🏁 Conclusion

Circular Linked Lists are useful when data needs to be processed in a loop.

👉 They are widely used in real-world systems and interview problems.

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