251. Flatten 2D Vector

最新推荐文章于 2021-09-22 14:42:08 发布

原创最新推荐文章于 2021-09-22 14:42:08 发布 · 344 阅读

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#LeetCode #Design #Flatten 2D Vector

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本文介绍了一种用于遍历二维向量的迭代器实现方法。通过使用Java语言，我们展示了如何创建一个能够平铺二维向量的迭代器，使得元素能够按照顺序逐一访问。

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Implement an iterator to flatten a 2d vector.

For example,
Given 2d vector =

[
  [1,2],
  [3],
  [4,5,6]
]

By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,2,3,4,5,6].

Follow up:
As an added challenge, try to code it using only iterators in C++ or iterators in Java.

首先的想法是保存peek的数，hasnext每次判断peek的数是不是为null，next返回peek的数。代码如下：

public class Vector2D implements Iterator<Integer> {
    Iterator<Integer> Rowiter;
    Iterator<List<Integer>> Coliter;
    Integer next;

    public Vector2D(List<List<Integer>> vec2d) {
        Coliter = vec2d.iterator();
        if (Coliter.hasNext()) {
            Rowiter = Coliter.next().iterator();
            while (!Rowiter.hasNext() && Coliter.hasNext()) {
                Rowiter = Coliter.next().iterator();
            }
            next = Rowiter.hasNext()? Rowiter.next(): null;
        }
    }

    @Override
    public Integer next() {
        Integer res = next;
        if (Rowiter.hasNext()) {
            next = Rowiter.next();
        } else { 
            while (!Rowiter.hasNext() && Coliter.hasNext()) {
                Rowiter = Coliter.next().iterator();
            }
            next = Rowiter.hasNext()? Rowiter.next(): null;
        }
        return res;
    }

    @Override
    public boolean hasNext() {
        return next != null;
    }
}

/**
 * Your Vector2D object will be instantiated and called as such:
 * Vector2D i = new Vector2D(vec2d);
 * while (i.hasNext()) v[f()] = i.next();
 */

但是可以简化代码，因为next和hasnext函数Iterator都有，可以直接用。代码如下：

 public class Vector2D implements Iterator<Integer> {
    private Iterator<List<Integer>> rec;
	private Iterator<Integer> n;
	
    public Vector2D(List<List<Integer>> vec2d) {
        rec = vec2d.iterator();
    }

    @Override
    public Integer next() {
        return n.next();
    }

    @Override
    public boolean hasNext() {
        while((n==null||!n.hasNext())&&rec.hasNext())
        	n = rec.next().iterator();
        return n!=null&&n.hasNext();
    }
}

/**
 * Your Vector2D object will be instantiated and called as such:
 * Vector2D i = new Vector2D(vec2d);
 * while (i.hasNext()) v[f()] = i.next();
 */