Remove Duplicates from a Sorted Linked List

Introduction

When working with linked lists, handling duplicates is a common task. This problem becomes easier when the list is already sorted, because duplicate values will always appear next to each other.

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Problem Statement

Given a sorted singly linked list, remove all duplicate nodes so that each element appears only once.

Return the modified linked list.

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Example

Input:

2 → 2 → 4 → 5

Output:

2 → 4 → 5

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Key Insight

Since the list is sorted:

• Duplicate elements will be adjacent
• So we only need to compare the current node with the next node

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Approach

We traverse the linked list and:

• If current value == next value → skip the next node
• Else → move forward

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Steps

1. Start from head
2. While current and current.next exist:

• If values are same → remove duplicate
• Else → move to next node

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Python Implementation

```python id="4nq7u9"
class ListNode:
def init(self, val=0, next=None):
self.val = val
self.next = next

def remove_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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## Step-by-Step Example

For:



```id="5czl2y"
2 → 2 → 4 → 5

• Compare 2 and 2 → duplicate → remove one
• Move to 2 → compare with 4 → different
• Continue till end

Final result:

2 → 4 → 5

Key Points

• Works because list is sorted
• No extra space required
• Simple pointer manipulation
• Very common beginner problem

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Conclusion

Removing duplicates from a sorted linked list is a straightforward problem once you understand how linked list pointers work. Since duplicates are adjacent, we can solve it efficiently in a single pass.

This problem builds a strong foundation for more advanced linked list operations.