题解 | #NC53-删除链表的倒数第n个节点#

/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */
/***************************************************************************************
* 快慢双指针，left和right初始都指向链表头节点，right先走n步
* 如果移动n步后已达到最后一个节点，那么返回head->next节点
* 否则若right->next不为空，right向右移，且left也向右移，移动完成后left->next节点即为倒数第n个节点
*****************************************************************************************/
class Solution {
public:
    /**
     * 
     * @param head ListNode类 
     * @param n int整型 
     * @return ListNode类
     */
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        // write code here
        int i;
        struct ListNode *left = head;
        struct ListNode *right = head;
        
        if(head == NULL)
            return head;
        for(i = 0; i < n; i++)
            right = right->next;

        if(right == NULL)
            return head->next;
        
        while(right->next != NULL)
        {
            right = right->next;
            left = left->next;
        }
        
        left->next = left->next->next;
        return head;
    }
};