题解 | 删除有序链表中重复的元素-II

import java.util.*;

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

/**
 * NC24 删除有序链表中重复的元素-II
 * @author d3y1
 */
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
     * @return ListNode类
     */
    public ListNode deleteDuplicates (ListNode head) {
        return solution1(head);
        // return solution2(head);
    }

    /**
     * 链表
     * @param head
     * @return
     */
    private ListNode solution1(ListNode head){
        ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;
        ListNode pre = dummyHead;
        ListNode curr = pre.next;
        while(curr!=null && curr.next!=null){
            // 重复
            if(curr.val == curr.next.val){
                curr = curr.next;
                while(curr.next!=null && curr.val==curr.next.val){
                    curr = curr.next;
                }
                pre.next = curr.next;
            }
            // 不重复
            else{
                pre = curr;
            }
            curr = curr.next;
        }

        return dummyHead.next;
    }

    /**
     * 链表
     * @param head
     * @return
     */
    private ListNode solution2(ListNode head){
        ListNode dummyHead = new ListNode(-1);
        dummyHead.next = head;
        ListNode curr = dummyHead;
        int val;
        while(curr.next!=null && curr.next.next!=null){
            // 重复
            if(curr.next.val == curr.next.next.val){
                val = curr.next.val;
                while(curr.next!=null && curr.next.val==val){
                    curr.next = curr.next.next;
                }
            }
            // 不重复
            else{
                curr = curr.next;
            }
        }

        return dummyHead.next;
    }
}