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) {}
 * };
 */
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
        ListNode* dummy = new ListNode(0);
        dummy->next = head;
        ListNode* slow = head;
        ListNode* fast = head;
        ListNode* pre = dummy;
        while(n--) {
            if(fast) fast=fast->next;
        }
         //快慢指针同步，快指针到达末尾，慢指针就到了倒数第n个位置
        while(fast) {
            fast=fast->next;
            pre=slow;
            slow=slow->next;
        }
        ListNode* s = pre->next;
        pre->next = pre->next->next;
        s->next=nullptr;
        delete s;
        return dummy->next;
    }
};