题解 | #删除链表的倒数第n个节点#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 *	ListNode(int x) : val(x), next(nullptr) {}
 * };
 * 还是双指针的问题，关键的问题是边界的考虑。就是当n刚好是结点个数时的情况。
 */
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @param n int整型 
     * @return ListNode类
     */
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        // write code here
        if (head == nullptr) return nullptr;

        auto slow = head;
        auto fast = head;
        for (int i = 0; i < n; ++i)
          fast = fast->next;

        if (fast == nullptr) {
          auto ret = head->next;
          delete head;
          return ret;
        }
          
        while (fast->next != nullptr) {
          slow = slow->next;
          fast = fast->next;
        }

        auto temp = slow->next;
        slow->next = temp->next;
        delete temp;
        return head;
    }
};