Linked List problems

Rewiring pointers between nodes instead of shifting array elements.

1. Reverse Linked List (Easy)
2. Merge Two Sorted Lists (Easy)
3. Linked List Cycle (Easy)
4. Reorder List (Medium)
5. Remove Nth Node From End of List (Medium)
6. Copy List with Random Pointer (Medium)
7. Add Two Numbers (Medium)
8. Find the Duplicate Number (Medium)
9. LRU Cache (Medium)
10. Merge K Sorted Lists (Hard)