comefrom: <awangdev>4Sum_1.java
code: private String buildKey(List<Integer> list) {
  
          StringBuffer sb = new StringBuffer();
          for (int num : list) sb.append(num + "@");
          return sb.toString();
      }
masked: private String var_0 ( List < Integer > var_1 ) {
    StringBuffer var_2 = new StringBuffer ( ) ;
    for ( int var_3 : var_1 ) var_2 . append ( var_3 + "@" ) ;
    return var_2 . toString ( ) ;
  }
  