leetcode 19. 删除链表的倒数第 N 个结点

https://leetcode.cn/problems/remove-nth-node-from-end-of-list/

快慢指针 ， 审题！！！

 //注意审题  是倒数n个结点！！！
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        if(!head ||!head->next) {
            return NULL;
        }
        ListNode *fast = head, *slow = head;
        for(int i = 0; i < n; i ++) {
            fast = fast -> next;// fast比slow先走n步
        }
        if(fast == NULL) { // 删除头结点
            return head->next;
        }
        while(fast -> next) {
            fast = fast->next;
            slow = slow->next;
        }
        slow ->next= slow->next->next;
        return head;
    }
};