Remove Nth Node From End of List 解答

Question

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.

Solution -- One pass

Use two pointers, slow and fast. Fast pointer firstly move n steps. Then, when fast pointer reaches end, slow pointer reaches the node before deleted node.

 /**
  * 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 fast = head, slow = head;
         if (head == null)
             return head;
         while (n > 0) {
             fast = fast.next;
             n--;
         }
         // If remove the first node
         if (fast == null) {
             head = head.next;
             return head;
         }
         while (fast.next != null) {
             fast = fast.next;
             slow = slow.next;
         }
         slow.next = slow.next.next;
         return head;
     }
 }