删除链表的倒数第n个节点

学习目标：删除链表的倒数第n个节点

---

实现方法：

/**
 * 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
        if (head == NULL)
            return NULL;
        ListNode* res = new ListNode(0);
        res->next = head;
        
        //当前节点
        ListNode* cur = head;
        //前节点
        ListNode* pre = res;
        ListNode* fast = head;
        //先让fast快走N步；
        while (n--)
            fast = fast->next;
        //快慢指针同步，快指针到底最后，慢指针正好到了倒数第N个位置
        while (fast != NULL) {
            fast = fast->next;
            pre = cur;
            cur = cur->next;
        }
        //删除该位置的节点
        pre->next = cur->next;
        //返回头节点
        return res->next;
    }
};

---