Google – Iterator of Iterator

Google – Iterator of Iterator
Input一个list of iterator，设计一个SuperIterator。
[Solution]
Maintain一个current iterator

class SuperIterator<T> implements Iterator<T> {

  List<Iterator<T>> itList;

  Iterator<T> curr;

  int i;

  public SuperIterator(List<Iterator<T>> itList) {

    if (itList == null || itList.isEmpty()) {

      throw new IllegalArgumentException();

    }

    this.itList = itList;

    curr = itList.get(0);

  }

  @Override

  public boolean hasNext() {

    return curr != null && curr.hasNext();

  }

  @Override

  public T next() {

    T result;

    if (curr != null && curr.hasNext()) {

      result = curr.next();

    }

    else {

      while (i < itList.size() && !itList.get(i).hasNext()) {

        i++;

      }

      if (i < itList.size()) {

        curr = itList.get(i);

      }

      else {

        return null;

      }

      result = curr.next();

    }

    // update curr iterator

    while (i < itList.size() && !itList.get(i).hasNext()) {

      i++;

    }

    if (i < itList.size()) {

      curr = itList.get(i);

    }

    else {

      curr = null;

    }

    return result;

  }

}

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