Remove Nth Node From End of List

Problem

Given the head of a linked list, remove the nth node from the end of the list and return its head.

Examples

The brute-force approach

Two-pass: count the total length, then compute the position from the front (length - n), traverse again to remove it.

length = 0
curr = head
while curr:
    length += 1
    curr = curr.next

target = length - n
dummy = ListNode(0, head)
curr = dummy
for _ in range(target):
    curr = curr.next
curr.next = curr.next.next
return dummy.next

O(n) with two passes. Not slower in big-O terms, but the one-pass two-pointer approach is the expected solution.

Spotting the pattern

This is a Linked List problem. The key question to ask yourself:

If fast is n steps ahead of slow, and fast reaches the last node, where is slow?

Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.