Main.java:16: error: cannot find symbol
    	if(cur.length() == max*2){
    	      ^
  symbol:   method length()
  location: variable cur of type List<String>
Main.java:17: error: incompatible types: String cannot be converted to List<String>
        	ans.add(cur.toString());
        	                    ^
Main.java:21: error: cannot find symbol
        	cur.append('(');
        	   ^
  symbol:   method append(char)
  location: variable cur of type List<String>
Main.java:23: error: cannot find symbol
            cur.deleteCharAt(cur.length() - 1);
                                ^
  symbol:   method length()
  location: variable cur of type List<String>
Main.java:26: error: cannot find symbol
        	cur.append(')');
        	   ^
  symbol:   method append(char)
  location: variable cur of type List<String>
Main.java:28: error: cannot find symbol
            cur.deleteCharAt(cur.length() - 1);
                                ^
  symbol:   method length()
  location: variable cur of type List<String>
Main.java:32: error: incompatible types: List<String> cannot be converted to List<List<String>>
    	cb(ans,cur,n,0,0);
    	   ^
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
7 errors