comefrom: <awangdev>36. Valid Sudoku_1.java
code: private boolean helper(char c, Set<Character> set) {
  
          if (!set.contains(c)) set.add(c);
          else if (c != '.') return false;
          return true;
      }
masked: private boolean var_0 ( char var_1 , Set < Character > var_4 ) {
    if ( ! var_4 . contains ( var_1 ) ) var_4 . add ( var_1 ) ;
    else if ( var_1 != '.' ) return false ;
    return true ;
  }
  