04 Fast and Slow Pointers - Cycle Detection

Requirement - a Linked list or similar structure which can form cycles
Core Problem - Find if there are cycles in our LinkedList / Graph
Core Logic : Fast pointer moves 2 steps at a time thus is able loop the cycle if there is any, and stab the slow pointer on the back

Steps:

1. 1. Initialize two pointers, one moving one step at a time (slow) and the other moving two steps at a time (fast).
2. If there is a cycle, the fast pointer will eventually meet the slow pointer.
3. If the fast pointer reaches the end of the list, there is no cycle.

Sample Problem:

Detect if a linked list has a cycle.

LeetCode Problems:

1. Linked List Cycle (LeetCode #141)
2. Happy Number (LeetCode #202)
3. Find the Duplicate Number (LeetCode #287)