ZigzagIterator2.java

public class ZigzagIterator2 {
    
    public List<Iterator<Integer>> its;
    public int turns;

    /**
     * @param vecs a list of 1d vectors
     */
    public ZigzagIterator2(List<List<Integer>> vecs) {
        // initialize your data structure here.
        this.its = new ArrayList<Iterator<Integer>>();
        for (List<Integer> vec : vecs) {
            if (vec.size() > 0)
                its.add(vec.iterator());
        }
        turns = 0;
    }

    public int next() {
        // Write your code here
        int elem = its.get(turns).next();
        if (its.get(turns).hasNext())
            turns = (turns + 1) % its.size();
        else {
            its.remove(turns);
            if (its.size() > 0) 
                turns %= its.size();
        }
        return elem;
    }

    public boolean hasNext() {
        // Write your code here
        return its.size() > 0;        
    }
}