Data Structures

Lesson

Linked Lists have a 1st element, a 2nd element, and so on. This makes them similar to Arrays, but they're structured very differently.

Each node in a Linked List has a value `val`

and a pointer to the next node `next`

. The very start of the Linked List is called the "head". Here's an accurate drawing of a Linked List:

People like to use shorthand, so you'll often see them drawn like this instead, with the values drawn inside of the nodes:

It's generally slow to read from a Linked List because you need to start at the first node and step through many other nodes. For example, here's how you read the 4th element in the linked list:

Reading takes worst-case $O(n)$ time, where $n$ is the number of nodes in the Linked List. The same thing holds for writing, inserting and deleting.

Read/Write Time $O(n)$

Insert/Delete Time $O(n)$

So why bother using a Linked List, if they seem slower than Arrays? The idea is that you can quickly insert and delete an element, if you're already standing at a node in the Linked List.

You can insert quickly if you're standing at a node:

You can also delete quickly if you're standing at a node:

Insert/Delete Time $O(1)$ if you're already standing at the node.

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