删除链表中倒数第n个节点

给定一个链表，删除链表中倒数第n个节点，返回链表的头节点。



 注意事项

链表中的节点个数大于等于n

您在真实的面试中是否遇到过这个题？ Yes
样例
给出链表1->2->3->4->5->null和 n = 2.

删除倒数第二个节点之后，这个链表将变成1->2->3->5->null.

/**
 * Definition of ListNode
 * class ListNode {
 * public:
 *     int val;
 *     ListNode *next;
 *     ListNode(int val) {
 *         this->val = val;
 *         this->next = NULL;
 *     }
 * }
 */
class Solution {
public:
    /**
     * @param head: The first node of linked list.
     * @param n: An integer.
     * @return: The head of linked list.
     */
    ListNode *removeNthFromEnd(ListNode *head, int n) {
        // write your code here
        ListNode* start = new ListNode(0);
        start -> next = head;
        ListNode* fast = start;
        ListNode* slow = start;
        int i = 1;
        while(fast != NULL && i<=n) {
            fast = fast->next;
            i++;
        }
        while(fast->next != NULL) {
            fast  = fast->next;
            slow = slow->next;
        }
        
        slow->next = slow->next->next;
        return start -> next;
        
    }
};