299. Remove Nth Node From End of List

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

This classic two-pointer problem requires you to find and remove a node at a specific position from the end, ideally in a single pass.

Examples

// List: 1 → 2 → 3 → 4 → 5,  n = 2
// Remove 4 (2nd from end)
// Result: 1 → 2 → 3 → 5