Merge Two Sorted Linked Lists | Dataford Interview Questions

Merge two sorted linked lists

Asked in the Interview 2 stage. Given the heads of two singly linked lists sorted in ascending order, merge them into one sorted linked list by reusing the existing nodes.

Contract

Implement merge_two_lists(l1, l2), where each input is either a ListNode head or None. Return the head of the merged list. Each ListNode has val and next attributes. The output must preserve duplicate values and use no new list nodes.

Constraints

Each input list contains at most 1,000 nodes
Node values are integers
Both lists are sorted in nondecreasing order
The output reuses the input nodes and creates no new list nodes

Function Signature

def merge_two_lists(l1, l2):

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Problem