[数据结构与算法]leetcode19删除链表的倒数第N个节点

给定一个链表，删除链表的倒数第 n 个节点，并且返回链表的头结点。
示例：
给定一个链表: 1->2->3->4->5, 和 n = 2.
当删除了倒数第二个节点后，链表变为 1->2->3->5
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        int length = 0;
        ListNode current = head;
        while(current != null){
            length++;
            current = current.next;
        }
        length -= n;
        current = dummy;
        while(length > 0){
            length--;
            current = current.next;
        };
        current.next = current.next.next;
        return dummy.next;
	}
}

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