Put all the values in the linklist into a hashmap with each spot equal to its location on the linked list then using two pointers, one at 1 and the other at size of the link list compare the values at both pointers if equal, add one to the smaller one and remove one from the other compare the values at both pointers do until both pointer value are the same or values at the pointer are not equal.

I would try to see what type of linked list it is. If singly, the stack method would work well. For doubly, traverse to the end of the list and compare it to the front. Traverse inwards until left node equals the right node.