题解 | #删除链表的倒数第n个节点#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param head ListNode类
     * @param n int整型
     * @return ListNode类
     */
    private ListNode FindKthToTail (ListNode pHead, int k) {
        // write code here
        if (pHead == null) return null;
        ListNode fast, slow;
        fast = pHead;
        slow = pHead;
        int n = 1;
        while (fast.next != null) {
            fast = fast.next;
            n = n + 1;
        }
        if (n - k < 0) return null;
        for (int i = 0; i < n - k; i++) {
            slow = slow.next;
        }
        return slow;
    }

    public ListNode removeNthFromEnd (ListNode head, int n) {
        // write code here
        ListNode pre;
        ListNode dummyNode = new ListNode(-1);
        dummyNode.next = head;
    
        pre = FindKthToTail(dummyNode, n+1);
        pre.next = pre.next.next;
        return dummyNode.next;
    }
}