Leetcode 281 Zigzag Iterator

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

For example, given two 1d vectors:

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].

Follow up: What if you are given k 1d vectors? How well can your code be extended to such cases?

Clarification for the follow up question - Update (2015-09-18):
The "Zigzag" order is not clearly defined and is ambiguous for k > 2 cases. If "Zigzag" does not look right to you, replace "Zigzag" with "Cyclic". For example, given the following input:

[1,2,3]
[4,5,6,7]
[8,9]

It should return [1,4,8,2,5,9,3,6,7].
Solution 1: a simple design question.

 public class ZigzagIterator {  
   private int i, j;  
   private int n;  
   List<Integer> v1;  
   List<Integer> v2;  
   public ZigzagIterator(List<Integer> v1, List<Integer> v2) {  
     this.v1=v1;  
     this.v2=v2;  
     i=0;  
     j=0;  
     n=Math.max(v1.size(),v2.size());  
     if (v1.size()==0) i++;  
   }  
   public int next() {  
     int res=0;  
     if (i==0) {  
       res=v1.get(j);  
       if (j>=v2.size()) j++;  
       else i++;  
     }  
     else {  
       res=v2.get(j);  
       j++;  
       if (j<v1.size()) i=0;  
     }  
     return res;  
   }  
   public boolean hasNext() {  
     return j<n;  
   }  
 }