Remove Nth Node from End

Problem

Given the head of a singly linked list and an integer n, remove the nth node from the end and return the (possibly new) head.

Constraints

• 1 ≤ length ≤ 30
• 1 ≤ n ≤ length

Approach — Two Pointers

This is a Two Pointers problem. The idea: walk two indices through the data together (or toward each other), turning an O(n²) pair search into one linear pass. Work through the reference code below line by line, then re-derive it yourself in the editor — that's how the pattern sticks.

Complexity: O(n) time, O(1) extra space.

Solution code

Python

class Solution:
    def removeNthFromEnd(self, head, n):
        dummy = ListNode(0, head)
        fast = slow = dummy
        for _ in range(n):
            fast = fast.next
        while fast.next:
            fast = fast.next
            slow = slow.next
        slow.next = slow.next.next
        return dummy.next

Java

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode fast = dummy, slow = dummy;
        for (int i = 0; i < n; i++) fast = fast.next;
        while (fast.next != null) { fast = fast.next; slow = slow.next; }
        slow.next = slow.next.next;
        return dummy.next;
    }
}

Practice it

Reading a solution isn't the same as being able to write it under pressure. Open this problem in the in-browser editor, hide the solution, and solve it from scratch — your code runs against real test cases instantly.