comefrom: <awangdev>1203. Sort Items by Groups Respecting Dependencies_3.java
code: private Map<Integer, List<Integer>> buildItemGraph(List<Integer> items, List<List<Integer>> beforeItems) {
  
          Map<Integer, List<Integer>> graph = new HashMap<>();
          for (int i : items) {
              for (int item : beforeItems.get(i)) {
                  graph.putIfAbsent(item, new ArrayList<>());
                  graph.get(item).add(i);
              }
          }
          return graph;
      }
masked: private Map < Integer , List < Integer >> var_2 ( List < Integer > var_3 , List < List < Integer >> var_4 ) {
    Map < Integer , List < Integer >> var_7 = new HashMap < > ( ) ;
    for ( int var_8 : var_3 ) {
      for ( int var_10 : var_4 . get ( var_8 ) ) {
        var_7 . putIfAbsent ( var_10 , new ArrayList < > ( ) ) ;
        var_7 . get ( var_10 ) . add ( var_8 ) ;
      }
    }
    return var_7 ;
  }
  