BM9.java

package NiukeTOP101;

public class BM9 {
    /**
     *
     * @param head ListNode类
     * @param n int整型
     * @return ListNode类
     */
    public ListNode removeNthFromEnd (ListNode head, int n) {
        //添加表头
        ListNode res = new ListNode(-1);
        res.next = head;
        //当前节点
        ListNode cur = head;
        //前序节点
        ListNode pre = res;
        ListNode fast = head;
        //快指针先行n步
        while(n != 0){
            fast = fast.next;
            n--;
        }
        //快慢指针同步，快指针到达末尾，慢指针就到了倒数第n个位置
        while(fast != null){
            fast = fast.next;
            pre = cur;
            cur = cur.next;
        }
        //删除该位置的节点
        pre.next = cur.next;
        //返回去掉头
        return res.next;
    }
}