Remove Duplicates from List | Dataford Interview Questions

Samsung Semiconductor diagnostic pipelines may represent ordered event identifiers as a singly linked list. Implement an in-place algorithm that removes every duplicate node while preserving the first occurrence and the relative order of remaining nodes.

Use the following node model:

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

Implement remove_duplicates(head). The function receives the head node and must return the head of the modified list. A linked list such as [3, 1, 3, 2, 1] is represented in examples and tests by its serialized value array, but the submitted function operates on ListNode objects.

Do not allocate replacement nodes or use a set, dictionary, list, or other value-based buffer. Rewire existing next pointers directly. Keep the first node containing each value.

Constraints

0 <= number of nodes <= 10^4
-10^9 <= node.val <= 10^9
The input is a singly linked list of ListNode objects
Do not use auxiliary storage proportional to the number of nodes

Function Signature

def remove_duplicates(head):

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