时间轴

2025-11-20

init

题目：

P19 删除链表的倒数第 N 个结点

https://leetcode.cn/problems/remove-nth-node-from-end-of-list/description/?envType=study-plan-v2&envId=top-interview-150

注意特殊情况，即要删除的是头节点

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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)
	{
		//双指针，当l从head开始，r=从head+n开始
		ListNode *l = head;
		ListNode *r = head;
		ListNode *p;

		for (int i = 0; i < n; i++) {
			r = r->next;
		}
		if (r == nullptr) { // n == sz
			p = head;

			head = head->next;
			delete p;
			return head;
		}

		while (r->next != nullptr) {
			r = r->next;
			l = l->next;
		}
		p = l->next;
		l->next = p->next;
		delete p;
		return head;
	}
};