19.删除链表的倒数第-n-个结点.cpp

/*
 * @lc app=leetcode.cn id=19 lang=cpp
 *
 * [19] 删除链表的倒数第 N 个结点
 * 
 * 头节点需要变化或需要额外判定，可以使用虚拟头节点
 */

// @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) {
        auto dummy = new ListNode();
        dummy->next = head;
        auto *fast = dummy, *slow = dummy;
        while (n--) fast = fast->next;
        while (fast->next) {
            fast = fast->next;
            slow = slow->next;
        }
        slow->next = slow->next->next;
        return dummy->next;
    }
};
// @lc code=end