Algorithms / Linked List Pointer Updates

Least You Need to Know: Linked-List Pointer Updates and Local Rewiring

Linked-list problems are about **preserving access while changing arrows**. Because each node only knows its next pointer, interviews reward students who save the next node before rewiring and who reason locally about what each pointer update does to the rest of the list.

The least you need to know

In a singly linked list, changing one `next` pointer can disconnect the remaining suffix if you did not save it first.
Pointer rewiring is local: you usually only touch a constant number of nodes at a time.
When the first node changes, you often need to update the head pointer too.
Null checks matter because tail nodes do not have a valid `next` node.
A hand-drawn picture of arrows is often the fastest way to reason safely.

Key notation

head pointer to the first node

node.next the next node after node

saved_next temporarily stored successor before rewiring

Tiny worked example

Suppose `head -> 3 -> 5 -> 8` and you want to remove the node `5`.
First keep a pointer to the node before it or to the current node being examined.
Then redirect that previous node so it points to `8` instead of `5`.
The key idea is that the rest of the list stays reachable because you rewired the correct arrow.

Common mistakes

Students often overwrite `current.next` before remembering where the rest of the list went.
Students often forget that changing the first node requires returning a new head.
Students often dereference `current.next` without first checking whether `current` is null.

How to recognize this kind of problem

The prompt talks about inserting, deleting, or splicing nodes from a singly linked list.
The algorithm only needs local pointer changes, not random indexing.
A picture of arrows makes the state easier to verify than array-style reasoning.