🔗 Remove Duplicates from a Sorted Linked List

Removing duplicates from a linked list is a common problem that helps you understand pointer traversal and in-place modification.

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📌 Problem Statement

Given the head of a sorted linked list, remove all duplicate elements so that each value appears only once.

Return the updated linked list.

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🔍 Example

Input:
2 → 2 → 2 → 2

Output:
2

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🧠 Intuition

Since the list is already sorted:

👉 Duplicate elements will always be next to each other

So we can:

• Compare current node with next node
• Skip duplicates by adjusting pointers

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🔄 Approach (Iterative)

Step-by-Step:

1. Start from the head
2. Traverse the list
3. If current value equals next value:

• Skip the next node

  1. Else:

• Move forward

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💻 Python Code

```python id="dup1"
class ListNode:
def init(self, val=0, next=None):
self.val = val
self.next = next

def delete_duplicates(head):
current = head

while current and current.next:
    if current.val == current.next.val:
        current.next = current.next.next  # skip duplicate
    else:
        current = current.next

return head

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🧾 Dry Run

For:
2 → 2 → 2 → 2

Steps:

* Compare first two → same → skip
* Compare next → same → skip
* Continue until only one node remains

Final:
2

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⚡ Complexity

Time Complexity: O(n)
Space Complexity: O(1)

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🔥 Why This Works

* Sorted property ensures duplicates are adjacent
* Only one traversal needed
* No extra space used

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⚠️ Edge Cases

* Empty list
* Single node
* All elements same

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🏁 Conclusion

This problem teaches:

* Pointer manipulation
* Efficient traversal
* In-place linked list operations