How to delete the penultimate node of a linked list by List

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Problem: delete the penultimate node of the linked list

Title

Given a linked list, delete the penultimate node of the linked list and return the header node of the linked list.

Example:

Given a linked list: 1-> 2-> 3-> 4-> 5, and n = 2.

When the penultimate node is deleted, the linked list becomes 1-> 2-> 3-> 5

Description:

The given n guarantee is valid.

Advanced:

Can you try to do it with a scan?

Problem-solving ideas

Adopting double traversal can certainly solve the problem, but the problem requires us to traverse and solve the problem at once, then we have to diverge our thinking.

We can imagine that if double pointers p and Q are set, when Q points to the end of the NULL,p and the number of elements separated by Q is n, then deleting the next pointer to p completes the requirement.

Set the virtual node dummyHead to point to head

Set double pointers p and Q, which initially point to the virtual node dummyHead

Move Q until the number of elements separated by p and Q is n

Move p and Q at the same time until Q points to NULL

Point the next node of p to the next node

Animation demonstration

The animation GIF is a little big. Please wait a little while to load and display ^ _ ^.

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