Zigzag Iterator

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

• Time: O(n)
• Space: O(1)

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

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

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

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