public static String longestTwoUniqueSubStr(String str){
		List<String> chars = new ArrayList<String>();
		String maxSubString = "";
		String current = "";
		int i=0;
		for(char c: str.toCharArray()){
			chars.clear();
			chars.add(c + "");
			current = c + "";
			
			for(int j = i+1; j <str.length(); j++){
				if(chars.contains(str.charAt(j) + "")){
					current = current + str.charAt(j);
					if(current.length() > maxSubString.length()){
						maxSubString = current;
					}
				}
				else if(chars.size() == 1){
					chars.add(str.charAt(j) + "");
					current = current + str.charAt(j);
					if(current.length() > maxSubString.length()){
						maxSubString = current;
					}
				}else{
					if(current.length() > maxSubString.length()){
						maxSubString = current;
					}
					current = "";
					break;
				}
			}
			
			i++;
		}
		return maxSubString;
	}