Remove Nth Node From End of List.cpp

/**
 * 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) {
        ListNode* helper = new ListNode(-1);
        helper->next = head;
        auto fast = head, slow = helper;
        while(n--)fast = fast->next;
        while(fast)
        {
            fast = fast->next;
            slow = slow->next;
        }
        auto tmp = slow->next;
        slow->next = tmp->next;
        tmp->next = nullptr;
        return helper->next;
    }
};