Google – String Appear Only in One List

Google – String Appear Only in One List
给k个list of strings, 找出只在一个list里出现的string

  public List<String> appearOnce(List<List<String>> strings) {

    List<String> result = new ArrayList<>();

    Set<String> set = new HashSet<>();

     

    for (List<String> strs : strings) {

      Set<String> local = new HashSet<>();

      for (String str : strs) {

        local.add(str);

      }

      for (String str : local) {

        if (set.contains(str)) {

          set.remove(str);//???

        }

        else {

          set.add(str);

        }

      }

    }

     

    result.addAll(set);

    return result;

  }

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