力扣 19. 删除链表的倒数第 N 个结点

题目描述：

给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。

解析：
双指针：图片是删除倒数第二个节点

Java:

public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode n1 = dummy;
        ListNode n2 = dummy;
        for(int i = 0; i <= n; i++) {
            n2 = n2.next;
        }
        while(n2 != null) {
            n1 = n1.next;
            n2 = n2.next;
        }
        n1.next = n1.next.next;
        return dummy.next;
    }

JavaScript:

var removeNthFromEnd = function(head, n) {
    let dummy = new ListNode();
    dummy.next = head;
    let n1 = dummy;
    let n2 = dummy;
    for(let i = 0; i <= n; i++) {
        n2 = n2.next;
    }
    while(n2 !== null) {
        n1 = n1.next;
        n2 = n2.next;
    }
    n1.next = n1.next.next;
    return dummy.next;
};