19. Remove Nth Node From End of List

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

Example:

Given linked list: 1->2->3->4->5, and n = 2.

After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:

Given n will always be valid.

Follow up:

Could you do this in one pass?

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        System.out.println(head.val);
        if (head == null || head.next == null) return null;
        
        ListNode p1 = head;
        for (int i = 0; i < n; ++i) {
           
            p1 = p1.next;
        }
        if (p1 == null) return head.next;
        
        ListNode p2;
        for (p2 = head; p1.next != null; p1 = p1.next) {
            p2 = p2.next;
        }
        p2.next = p2.next.next;
        return head;
    }
}