Given a circular linked list, implement an algorithm that returns the node at the beginning of the loop.
how to solve
If I can use extra space, I can solve this very easily. I can justly use a hash table to detect if the element is appeared or not.
Next, I want to consider this problem without using that data structure. I took the following steps.
- Create two pointers, FastPointer and SlowPointer.
- Move fastPointer at a rate of 2 steps and SlowPointer at a rate of 1 step.
- When they collide, move SlowPointer to LinkedListHead. Keep FastPointer where it is.
- Move Slow Pointer and FastPointer at a rate of one step. Return the new collision point
without using extra space.
code2(with using map)
with using hash map.