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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* removeNthFromEnd(ListNode* head, int n) {
if(n <= 0)
return head;
//创建一个虚拟头节点
ListNode *dummyHead = new ListNode(-1);
dummyHead->next = head;
ListNode *p, *q;
p = q = dummyHead;
//p先走n步
for(size_t i = 0; i < n && p != nullptr; i++)
{
p = p->next;
}
//如果确实p能走n步,那说明链表中至少有n个元素,这时才能进行删除操作,否则要直接返回原链表
if(p == nullptr)
return head;
//p和q一起走,直到p->next = nullptr,此时q->next正是要删除的节点
while(p->next != nullptr)
{
p = p->next;
q = q->next;
}
//删除节点
q->next = q->next->next;
return dummyHead->next;
}
};