Links in doubly linked list can be memory optimized using XOR based list.
A variant of the list called Skip list which provides less than O(n) for search operations. Read more.
Another variant is called self organizing list which optimizes the search by placing the frequently visited nodes in the beginning of the list and hence reducing the time complexity.
Problems on singly linked list, leverage the following strategy
Recursion – Can be subsitute for the stack.
Fast and slow pointers.
Iteration – Previous, current, next pointers.
Making changes in the node.
Using hash.
In case of 2 linked lists, take traversal head of both.
For reversing, you could use recursion or traversal. In case of traversal, assign current.next to previous.
In singly linked list, if the value of the current node depends on the rest of the nodes, reverse the list first, operate on it and then reverse it back.
Quick sort is possible with singly linked list.
Doubly linked list.
Reversing requires just swapping of previous and next pointers.
