Intersection of Two Linked Lists

Two singly linked lists may merge: from some node on, they share the same nodes (the same objects in memory, not just equal values) until the end. Find the node where they meet.

Input:

• line 1: a b c — list A has a nodes of its own, list B has b nodes of its own, and then both continue into c shared nodes
• line 2: the a values of A's own part (may be empty)
• line 3: the b values of B's own part (may be empty)
• line 4: the c values of the shared part (may be empty)

The starter code builds the real structure: A = own part of A → shared part, B = own part of B → the same shared nodes.

Output: the positions of the meeting node: i j, where i is its 0-based index in list A and j its index in list B — or none if the lists don't meet.

Constraints: 0 ≤ a, b, c ≤ 3·10⁴, 1 ≤ a + c, 1 ≤ b + c; values are between 1 and 10⁵ and may repeat, so compare nodes, not values.

The trick: walk pointer p through A then B, and q through B then A. They travel the same total distance, so they reach the meeting node at the same moment — or both reach the end (null) together. Count steps to get the indices.