Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 2->3.

 

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
    	if (head == null) {
    		return head;
    	}
    	ListNode temp = new ListNode(0);
    	temp.next = head;
    	ListNode pre = temp;
    	ListNode cur = head;
    	ListNode nex = head.next;
    	boolean flag = false;
    	while (nex != null) {
    		if (cur.val == nex.val) {
    			flag = true;
    			nex = nex.next;
    			if (nex == null) {
    				pre.next = null;
    			}
    		} else {
    			if (flag) {
    				pre.next = nex;
    				flag = false;
    			} else {
    				pre = cur;
    			}
    			cur = nex;
    			nex = nex.next;
    		}
    	}
    	return temp.next;
    }
}