19. 删除链表的倒数第N个节点

class Solution {
    public ListNode removeNthFromEnd(ListNode head, int n) {
        // 创建哑节点，方便处理头节点可能被删除的情况
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        
        // 初始化快慢指针
        ListNode fast = dummy;
        ListNode slow = dummy;
        
        // 快指针先前进n+1步
        for (int i = 0; i <= n; i++) {
            fast = fast.next;
        }
        
        // 快慢指针同时前进，直到快指针到达链表末尾
        while (fast != null) {
            fast = fast.next;
            slow = slow.next;
        }
        
        // 此时慢指针指向要删除节点的前一个节点，执行删除操作
        slow.next = slow.next.next;
        
        return dummy.next;
    }
}