Solve linked list, tree, and grid problems

Problem A — Cycle start in a singly linked list You receive the head of a singly linked list that may or may not loop back on itself. Identify the node at which the loop first begins and return that node; when the list is acyclic, return null. A "cycle" here means that following next pointers from some node eventually revisits an earlier node; the cycle entry is the first node reached twice when walking from head. The traversal must run in linear time and use only $$O(1)$$…