Question

在Java中展平迭代器的迭代器。如果输入为[[1,2]，[3，[4,5]]，6]，则应返回[1,2,3,4,5,6]。实现hasNext（）和next（）。内部迭代器或列表为空时要小心。我认为我的代码不适用于多级内部列表。

public class FlattenList {
int index = 0;  // keep an index to indicate where the current accessed element is
List<Integer> flattenedList = new ArrayList<>();    // flattenedList
public FlattenList(List<List<Integer>> lists){  
    for(List<Integer> list : lists){    // add all inner list to our underlying list.
        flattenedList.addAll(list);
    }
}
public boolean hasNext(){   // check if the index has exceeded the list size
    return flattenedList.size() > index? true : false; 
}
public Integer next(){  // return the next element, and increment the index
    Integer result = flattenedList.get(index);
    index++;
    return result;
}

}

Answer 1

所以基本上这就像写一个树的深度优先遍历。该树的叶节点是数字，所有内部节点都被建模为迭代器。这是一些伪代码：

void flatten(Iterator<Object> iterator, List<Integer> flattenedList) {
    for (Object o : iterator)  {
        if (o instanceof Iterator) {
          flatten((Iterator) o, flattenedList);
        } else {
          flattenedList.add((Integer) o);
        }
     }
}

Answer 2

在这里，我会为你开始：

public <T> Iterator<T> flatten(final Iterator<Iterator<T>> iterators) {
    if (iterators == null) {
        throw new IllegalArgumentException("iterators can't be null");
    }

    return new Iterator<>() {
        @Override
        public boolean hasNext() {
            throw new UnsupportedOperationException("Not implemented: hasNext");
        }

        @Override
        public T next() {
            throw new UnsupportedOperationException("Not implemented: next");
        }
    };
}

现在你只是做那种讨厌的脑力劳动，你就会完成。

修改

如果您不习惯这种语法，请稍微简单一点：

public <T> Iterator<T> flatten(final Iterator<Iterator<T>> iterators) { return new MyFlatteningIterator<>(iterators); } public class MyFlatteningIterator<T> implements Iterator<T> { private final Iterator<Iterator<T>> iterators; public MyFlatteningIterator(final Iterator<Iterator<T>> iterators) { if (iterators == null) { throw new IllegalArgumentException("iterators can't be null"); } this.iterators = iterators; } @Override public boolean hasNext() { throw new UnsupportedOperationException("Not implemented: hasNext"); } @Override public T next() { throw new UnsupportedOperationException("Not implemented: next"); } }

在Java中展平迭代器的迭代器

2 个答案: