🚀 Introduction

Deleting a node in a Linked List means removing a specific node and updating the links (pointers) so the list remains connected.

👉 Unlike arrays, no shifting is required — just pointer updates.

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🔹 Linked List Structure

[Data | Next] → [Data | Next] → [Data | Next] → NULL

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🔹 Ways to Delete a Node

1. Delete by Value
2. Delete by Position
3. Delete First Node
4. Delete Last Node

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🔹 1. Delete First Node

💡 Concept

• Move head to next node

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🧾 Example

Before:

10 → 20 → 30 → NULL

After:

20 → 30 → NULL

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⚡ Complexity

👉 O(1)

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🔹 2. Delete Last Node

💡 Concept

• Traverse to second last node
• Set next = NULL

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🧾 Example

Before:

10 → 20 → 30 → NULL

After:

10 → 20 → NULL

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⚡ Complexity

👉 O(n)

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🔹 3. Delete by Value

💡 Concept

• Find node with given value
• Link previous node to next

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🧾 Example

Before:

10 → 20 → 30 → 40 → NULL

Delete value = 30

After:

10 → 20 → 40 → NULL

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⚡ Complexity

👉 O(n)

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🔹 4. Delete by Position

💡 Concept

• Traverse to position – 1
• Skip the node

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🧾 Example

Before:

10 → 20 → 30 → 40 → NULL

Delete position 2

After:

10 → 30 → 40 → NULL

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⚡ Complexity

👉 O(n)

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⚙️ Algorithm (Delete by Value)

1. If head is NULL → return
2. If head.data == value → head = head.next
3. Traverse list:
    if temp.next.data == value:
        temp.next = temp.next.next
        break

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🧑‍💻 PHP Implementation

<?phpclass Node {
    public $data;
    public $next;    public function __construct($data) {
        $this->data = $data;
        $this->next = null;
    }
}class LinkedList {
    public $head;    // Delete by value
    public function deleteByValue($value) {
        if ($this->head == null) return;        // If head is to be deleted
        if ($this->head->data == $value) {
            $this->head = $this->head->next;
            return;
        }        $temp = $this->head;        while ($temp->next != null) {
            if ($temp->next->data == $value) {
                $temp->next = $temp->next->next;
                return;
            }
            $temp = $temp->next;
        }
    }    // Display
    public function display() {
        $temp = $this->head;
        while ($temp != null) {
            echo $temp->data . " → ";
            $temp = $temp->next;
        }
        echo "NULL";
    }
}?>

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⚡ Time Complexity Summary

Operation	Complexity
Delete First Node	O(1)
Delete Last Node	O(n)
Delete by Value	O(n)
Delete by Position	O(n)

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🎯 Key Points

✅ No shifting required
✅ Pointer manipulation is key
✅ Efficient for dynamic data

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🧠 Interview Tips

👉 Important edge cases:

• Empty list
• Single node
• Value not found

👉 Common questions:

• Delete nth node from end
• Delete node without head
• Remove duplicates

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🏁 Conclusion

Deleting a node is a core Linked List operation.

👉 Mastering this helps you:

• Understand pointer logic
• Solve advanced DSA problems
• Crack coding interviews