19.删除链表的倒数第N个节点

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(-1);

        dummy.next = head;

        ListNode slow = dummy;
        ListNode fast = dummy;

        for(int i = 1; i <= n; i++){
            fast = fast.next;
        }

        while(fast.next != null) {
            slow = slow.next;
            fast = fast.next;
        }

        slow.next = slow.next.next;

        return dummy.next;
    }
}