LeetCode OJ-- Remove Nth Node From End of List

https://oj.leetcode.com/problems/remove-nth-node-from-end-of-list/

remove倒数第n个节点

一般list remove node的题目，都要先设置一个 dummy 节点， dummy->next = head,最后返回 dummy->next。

因为有可能要删除的就是head节点，这样不用再额外判断了。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *removeNthFromEnd(ListNode *head, int n) {
        if(head==NULL || n<=0)
            return head;
        
        ListNode *dummy = new ListNode(-1);
        dummy->next = head;
        ListNode *fast = dummy, *slow = dummy;
    
        while(n--)
        {
            if(fast == NULL)
                return dummy->next;
            fast = fast->next;
        }
        while(fast->next)
        {
            fast = fast->next;
            slow = slow->next;
        }
        if(slow->next)
            slow->next = slow->next->next;
            
        return dummy->next;
    }
};