Moving forward k steps

To read the value at a given position, counting from 0, you need to advance across that many next pointers. Position 0 needs 0 hops, since it is the head itself. Position 1 needs 1 hop. In general, a loop running that many times takes you to the right node.

It is like walking down a corridor: to reach door 3 you pass three doors.

0 hops: the head is position 0.

k hops: leads to the node at position k.

Reach index 2 in list [10, 20, 30, 40]

curr

curr starts at head (index 0, val 10). Hop 1 of 2.

Move 1 of 3

What if the list is too short?

If the position is 5 but the list only has 3 nodes, the pointer will become null before you finish taking your hops. Trying to read anything from a null pointer is a crash.

So check that the pointer is not null before each hop, and again before reading the value. A negative position is invalid too.

Null check: if the pointer is null at any point, the position is out of bounds.

Negative position: answer minus one immediately.

In code

if index < 0:
    return -1
curr = head
for _ in range(index):
    if not curr:
        return -1
    curr = curr.next
return curr.val if curr else -1