Remove Nth Node From End of List

Classic LC 19 — remove the Nth-from-end node of a singly-linked list in one pass. Asked as the second phone-screen problem in a Sr SDE loop. Requirements Input: head of singly-linked list, integer n (1-indexed from the tail). Return the modified head after removing the n-th node from the end. Constraint: do it in one pass. Notes Two-pointer pattern: advance fast by n+1 steps then walk both pointers until fast is null. slow.next is the target's predecessor. A sentinel/dummy head removes the special case of deleting the original head. Edge cases: list of length 1, n == length, n == 1. Preparation Drill the sentinel-head pattern; it generalizes to a family of linked-list deletion problems. Verbalize the invariant ("after the first loop, fast is n ahead of slow") — interviewers grade clarity on this kind of problem more than the code.