Leetcode - Flatten 2D Vector

Screenshot from 2016-02-17 22:18:41.png

My code:

public class Vector2D {
    private int lineNum = 0;
    private int index = 0;
    private List> l;
    int k = 0;
    public Vector2D(List> vec2d) {
        l = vec2d;
        k = vec2d.size();
    }

    public int next() {
        int ret = l.get(lineNum).get(index);
        index++;
        if (index >= l.get(lineNum).size()) {
            index = 0;
            lineNum++;
        }
        return ret;
    }

    public boolean hasNext() {
        while (lineNum < k) {
            if (l.get(lineNum).size() != 0)
                return true;
            lineNum++;
        }
        return false;
    }
}

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

这道题目不是很难。但是一个corner case 一直卡住，也没能想出为什么。直到用了eclipse debug之后才知道。
如果 list 里面有空的list，但是他又算一行，所以 hasNext() 无法检测出来。
这个时候，index = 0，从他里面取出元素的话，会发生溢出。
然后我就想着从next里面规避这种情况。
**
但是，这个想法，是大错特错的！！
规避溢出的唯一思路，就是从 hasNext() 入手。next() 永远不需要考虑是否会溢出。直接取。
hasNext() 负责判断溢出！
**

Anyway, Good luck, RIchardo!

My code:

public class Vector2D implements Iterator {
    List> list = new ArrayList>();
    int counter = 0;
    int total = 0;
    public Vector2D(List> vec2d) {
        for (List temp : vec2d) {
            list.add(temp.iterator());
        }
        total = vec2d.size();
    }

    @Override
    public Integer next() {
        return list.get(counter).next();
    }

    @Override
    public boolean hasNext() {
        while (counter < total) {
            if (list.get(counter).hasNext()) {
                return true;
            }
            else {
                counter++;
            }
        }
        return false;
    }
}

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

这些还是可以用， List 的思路来做。
不难。

Anyway, Good luck, Richardo! -- 09/14/2016