19. Remove Nth Node From End of List

/**
 * 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) {
      ListNode dummy = new ListNode(-1);
      dummy.next = head;
      ListNode fast = head;
      ListNode slow = dummy;
      while(n > 0){
        fast = fast.next;
        n--;
      }
      
      while( fast != null){
        fast = fast.next;
        slow = slow.next;
      }
      
      slow.next = slow.next.next;
      return dummy.next;
    }
}

 

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?