LeetCode - Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

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

Solution:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(head == null || head.next == null) return head;
        ListNode cur = head.next;
        ListNode prev = head;
        while(cur != null){
            ListNode runner = head;
            while(runner != cur){
                if(runner.val == cur.val){
                        prev.next = cur.next;
                        cur = prev.next;
                        break;
                }
                runner = runner.next;
            }
            if(runner == cur){
                prev = cur;
                cur = cur.next;
            }    
        }
        return head;
    }
}