Remove Nth Node From End of List

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.

Solution: head---back------front------>NULL
　　　　　　　　　　| 　　　 |
　　　　　　　　　　---> n <----

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode *removeNthFromEnd(ListNode *head, int n) {
12         ListNode dummy(0), *back = &dummy, *front = &dummy;
13         dummy.next = head;
14         while(n--) front = front->next;
15         while(front->next) {
16             front = front->next;
17             back = back->next;
18         }
19         back->next = back->next->next;
20         return dummy.next;
21     }
22 };