How do you traverse a linked list starting from the head node?

You traverse a linked list starting from the head node by repeatedly following the pointers to the next node.

In more detail, a linked list is a linear data structure where each element is a separate object, known as a node. Each node contains a data field and a reference (also known as a link or pointer) to the next node in the sequence. The head node is the first node in the list, and it is from here that you begin to traverse the list.

To traverse a linked list, you start at the head node and follow the pointers from one node to the next until you reach the end of the list, which is signified by a null pointer. This is typically done using a loop. In each iteration of the loop, you access the data in the current node and then move to the next node by following the pointer.

Here is a simple example in pseudocode:

```
currentNode = headNode
while currentNode is not null
process currentNode.data
currentNode = currentNode.next
```

In this example, `currentNode` is a variable that keeps track of the node that is currently being processed. It starts out as the head node. The loop continues as long as `currentNode` is not null, which means that we have not yet reached the end of the list. Inside the loop, we first process the data in the current node. This could involve printing the data, adding it to a sum, or any other operation. Then we move to the next node by setting `currentNode` to `currentNode.next`.

This is the most basic way to traverse a linked list. There are more complex ways to traverse a linked list, such as in reverse order or in a circular linked list, but these require additional techniques. The basic principle, however, remains the same: start at the head node and follow the pointers.