Remove Nth Node From End of List

问题：删除距离末尾n个距离的结点
分析：先找出距离末尾n个距离的结点其距离开始的距离多少，然后再删除

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/**  * Definition for singly-linked list.  * struct ListNode {  *     int val;  *     ListNode *next;  *     ListNode(int x) : val(x), next(NULL) {}  * };  */ class Solution { public:     int front;     int dfs(ListNode *head,int n,int step)     {         if(head==NULL) return 0;         int h=dfs(head->next,n,step+1)+1;         if(h==n) { front=step;}         return h;     }     ListNode *removeNthFromEnd(ListNode *head, int n) {         if(head==NULL) return head;         front=0;         dfs(head,n,1);         ListNode *help = new ListNode(0);         help->next=head;         int t=1;         ListNode *ret=help;         while(1)         {             if(t==front)             {                 ret->next=head->next;                 delete head;                 break;             }             ret=ret->next;             head=head->next;             t++;         }         return help->next;     } };