删除有序链表中重复项（重复项保留）

简单的一次遍历

import java.util.*;
public class Solution {
    public ListNode deleteDuplicates (ListNode head) {
        if(head == null)
            return head;
        /*ListNode temp = head;
        ListNode pre = head;
        head = head.next;
        while(head != null){
            if(pre.val == head.val){
                pre.next = head.next;
            }else{
                pre = head;
            }
            head = head.next;
        }
        return temp;*/

        //节省点空间
        ListNode pre = head;
        while(pre.next != null){
            if(pre.val == pre.next.val){
                pre.next = pre.next.next;
            }else{
                pre = pre.next;
            }
        }
        return head;
    }
}