NC24 删除有序链表中重复的元素-II

三个指针 pre 指向当前节点的前一个 right指向重复元素的下一个元素 cur指向重复元素的头一个。

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode deleteDuplicates (ListNode head) {
        if(head == null) return null;
        ListNode phead = new ListNode(-1);
        phead.next = head;

        ListNode cur = head;
        ListNode right = head.next;
        ListNode pre = phead;

        while(cur.next != null ){
            if(cur.val == right.val){
                while(right != null && cur.val == right.val ) 
                {right = right.next;}
                pre.next = right;
            }else{
                pre = cur;
            }
            if(right == null) break;
            cur = right;
            right = cur.next;
        }

        return phead.next;
    }
}