删除链表的倒数第 N 个结点

[Sunny]

[Nasuke]

var removeNthFromEnd = function(head, n) {
    if(!head) return head
    let ret = new ListNode(null, head), p = ret, q = head
    while(n--) q = q.next
    while(q) q = q.next, p = p.next
    p.next = p.next.next

    return ret.next

};