LeetCode 19. Remove Nth Node From End of List

Question

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

https://leetcode.com/problems/remove-nth-node-from-end-of-list/

• Solution1

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode first = dummy, second = dummy;
        for (int i = 1; i <= n+1; i++)
            first = first.next;
        while(first != null){
            first = first.next;
            second = second.next;
        }
        second.next = second.next.next;
        return dummy.next;
    }
}

Complexity:

Time complexity: O(n)

Space complexity: O(1)