Maximum Sum Linked List from Two Sorted Linked Lists

Traverse the two sorted lists with pointers and two running sums. When values differ, advance the smaller value's pointer and add it to that list's sum. When values match, any optimal path reaching this common value should take the larger accumulated prefix, because both choices can continue from the same point afterward. Add the larger sum plus the common value to the answer, reset both sums, and advance both pointers. After either list ends, accumulate the remaining values in each list and add the larger suffix. If the task requires constructing a list rather than returning a sum, preserve nodes from the chosen segments and reconnect at common nodes, taking care not to create cycles. Clarify how duplicate common values are defined, since variants differ. Empty lists, no intersections, intersections at head, and a final shared value are important tests. Each node is visited at most once: O(m+n) time and O(1) extra space beyond any output list.