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
        if (head == nullptr) return NULL;
        ListNode* node = head;
        ListNode* pre = nullptr;
	  //计算链表长度
        int k = 0;
        while (node) {
            k++;
            node = node->next;
        }
        node = head;
        if (k == n) {	//如果要删除第一个节点
            head = head->next;
        } else {	//找到倒数第n个节点和前一个节点
            k = k - n;
            while (k--) {
                pre = node;
                node = node->next;
            }
            pre->next = node->next;
        }
        delete node;
        node = nullptr;
        return head;
    }
};