Linked List Merge Point Problem

You are given two singly linked lists and a third linked list, such that the two lists merge at some node of the third linked list. Determine the data value at the node where this merging begins. Return -1 if there is no merging.

Example:

Input:

First Linked List: a1 a2 c1 -1
Second Linked List: b1 b2 b3 c1 -1
Third Linked List: c2 c3 -1

Output:

c1

Constraints:

• The linked lists are represented by space-separated integers, terminated by -1.
• 0 <= Length of First List (N) <= 10^5
• 0 <= Length of Second List (M) <= 10^5
• 0 <= Length of Third List (K) <= 10^5
• -10^9 <= data value < 10^9, and data value is not -1

Note:

You don't need to print the result yourself, just implement the function to return the correct value.