/** * 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;    }};