【LeetCode】019. 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.

题解：

　　快慢指针。

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     ListNode *next;
  *     ListNode(int x) : val(x), next(NULL) {}
  * };
  */
 class Solution {
 public:
     ListNode* removeNthFromEnd(ListNode* head, int n) {
         if (!head)
             return head;
         ListNode dummy(-);
         dummy.next = head;
         ListNode* fast = &dummy, *slow = &dummy;

         while (n-- >=  && fast) fast = fast->next;

         while(fast) {
             fast = fast->next;
             slow = slow->next;
         }

         ListNode* tmp = slow->next;
         slow->next = slow->next->next;
         delete tmp;

         return dummy.next;
     }
 };