链表问题----删除倒数第K个节点

package com.test;

import com.test.ListNode;
import com.test.ListNodeDouble;

/**
 * Created by Demrystv.
 */
public class DelLastKNode {


    //删除单链表中的倒数第K 个节点
    public ListNode removeLastKthNodeInSingle(ListNode head, int lastKth){
        if (head == null || lastKth < 1){
            return null;
        }

        ListNode cur = head;
        while (cur != null){
            lastKth--;
            cur = cur.next;
        }
        if (lastKth == 0){
            head = head.next;
        }

        // 可以举例子：1 2 3 4 5 的倒数第4个节点
        if (lastKth < 0){
            cur = head;
            while (++lastKth != 0){
                cur = cur.next;
            }
            cur.next = cur.next.next;
        }
        return head;
    }


    // 删除双链表的倒数第K 个节点，原理与上面删除倒数第K个 节点的原理类似，主要是注意指针的连接
    public ListNodeDouble removeLastKthNodeInDouble(ListNodeDouble head, int lastKth){
        if (head == null || lastKth < 1){
            return null;
        }

        ListNodeDouble cur = head;
        while (cur != null){
            lastKth--;
            cur = cur.next;
        }

        if (lastKth == 0){
            head = head.next;
            head.last = null;
        }

        if (lastKth < 0){
            cur = head;
            while (++lastKth != 0){
                cur = cur.next;
            }
            ListNodeDouble newNext = cur.next.next;
            cur.next = newNext;
            if (newNext != null){
                newNext.last = cur;
            }
        }
        return head;
    }
}