[数据结构与算法]《每日一题》19. 删除链表的倒数第 N 个结点

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/**
 * 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* dhead = new ListNode(0);//创建虚拟头节点
        dhead->next = head;
        ListNode* slow = dhead;
        ListNode* fast = dhead;//双指针法
        while (fast != nullptr && n--){//
            fast = fast->next;
        }//提前fast指针
        fast = fast->next;//领先n+1步
        while (fast != nullptr){
            fast = fast->next;
            slow = slow->next;
        }//fast和slow指针一起前进
        slow->next = slow->next->next;

        return dhead->next;
    }
};