281. Zigzag Iterator z字型遍历

Given two 1d vectors, implement an iterator to return their elements alternately.

 

Example:

Input:
v1 = [1,2]
v2 = [3,4,5,6] 
Output: [1,3,2,4,5,6]
Explanation: By calling next repeatedly until hasNext returns false, 
the order of elements returned by next should be: [1,3,2,4,5,6].

思路：

去哪个里面找hasNext()呢？要用一个新的数据结构吧？好像也用不上stack啊
.iterator()这个接口本来就可以直接用

两边其实都可以找next()啊，所以就不知道究竟应该找哪边的。直接i j整个iterator互换就行了

public class ZigzagIterator {
    Iterator<Integer> i;
    Iterator<Integer> j;

    public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
        i = v1.iterator();
        j = v2.iterator();
    }

    public int next() {
        if (i.hasNext()) {
            Iterator<Integer> temp = i;
            i = j;
            j = temp;
        }

        return j.next();
    }

    public boolean hasNext() {
        return (i.hasNext() || j.hasNext());
    }
}

/**
 * Your ZigzagIterator object will be instantiated and called as such:
 * ZigzagIterator i = new ZigzagIterator(v1, v2);
 * while (i.hasNext()) v[f()] = i.next();
 */