/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} n
 * @return {ListNode}
 */
var removeNthFromEnd = function(head, n) {
    let empty_node=new ListNode(-1);
    empty_node.next=head;
    let p_slow=empty_node;
    let p_fast=empty_node;
    for(let i=0;i<=n;i++){
        p_fast=p_fast.next;
    }
    while(p_fast){
        p_fast=p_fast.next;
        p_slow=p_slow.next;
    }
    p_slow.next=p_slow.next.next;
    return empty_node.next;

};