1 mport java.util.ArrayList;
 2 import java.util.HashMap;
 3 public class Solution {
 4  HashMap<Character,Integer> map = new HashMap();
 5     ArrayList<Character> list = new ArrayList<Character>();
 6     //insert one char from stringstream
 7     public void Insert(char ch){
 8         if(map.containsKey(ch)){
 9             map.put(ch, map.get(ch)+1);
10         }else{
11             map.put(ch, 1);
12         }
13         list.add(ch);
14     }
15      public char FirstAppearingOnce()
16       {
17         char c = ‘#‘;
18         for(char key : list){
19             if(map.get(key) == 1){
20                 c = key;
21                 break;
22             }
23         }
24         return c;
25       }
26 }