lc19.java

// Given a linked list, remove the nth node from the end of list and return its head.
//
// For 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.
// Try to do this in one pass.
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
      ListNode dummy = new ListNode(0);
      dummy.next = head;
      ListNode res = dummy;
      ListNode p = dummy;
      ListNode q = dummy;
      while(n > 0){
        q = q.next; n--;
      }
      while(q.next != null){
        p = p.next;
        q = q.next;
      }
      p.next = p.next.next;
      return res.next;
    }
}