/*
 * @lc app=leetcode.cn id=19 lang=cpp
 *
 * [19] 删除链表的倒数第 N 个结点
 */

// @lc code=start
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ListNode *first = head;
        ListNode *second = head;
        int i = 0;
        for(i=0;i<n && second;i++){
            second = second->next;
        }
        if(!second) //删除头结点
        {
            head = head->next;
            return head;
        }

        while(second){
            if(!second->next)
                break;
            second = second->next;
            first = first->next;
        }
        
        //first 下一个节点为要删除的节点
        first->next = first->next->next;

        return head;
    }
};
// @lc code=end