题解 | #删除链表的倒数第n个节点#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param head ListNode类 
     * @param n int整型 
     * @return ListNode类
     */
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        // write code here
        ListNode* first = head; // first指针统计节点个数
        int count = 0;
        ListNode* second = head;    // second指针找到倒数第n+1个节点
        ListNode* result = new ListNode(-1);    // 最后返回result
        result->next = head;

        // 统计结点个数
        while(first){
            first = first->next;
            count++;
        }

        // 如果count等于n，说明删除第一个节点，直接返回result->next->next
        if(count == n) return result->next->next;
        // count大于n，则找到倒数第n+1个节点
        while(count != n + 1){
            second = second->next;
            count--;
        }
        ListNode* temp = second->next;  // 暂存倒数第n个节点
        second->next = temp->next;  // 让倒数第n+1个结点的next指向倒数第n个结点的next
        delete temp;    // 释放内存
        return result->next;
    }
};