Leetocode: 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?

Code (Java):

public class ZigzagIterator {
    private List<Integer> v1;
    private List<Integer> v2;
    private int i;
    private int j;
    private int listId;

    public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
        this.v1 = v1;
        this.v2 = v2;
        this.i = 0;
        this.j = 0;
        this.listId = 0;
    }

    public int next() {
        int result = 0;
        if (i >= v1.size()) {
            result = v2.get(j);
            j++;
        } else if (j >= v2.size()) {
            result = v1.get(i);
            i++;
        } else {
            if (listId == 0) {
                result = v1.get(i);
                i++;
                listId = 1;
            } else {
                result = v2.get(j);
                j++;
                listId = 0;
            }
        }
        
        return result;
    }

    public boolean hasNext() {
        return i < v1.size() || j < v2.size();
    }
}

/** * Your ZigzagIterator object will be instantiated and called as such: * ZigzagIterator i = new ZigzagIterator(v1, v2); * while (i.hasNext()) v[f()] = i.next(); */ Update on 5/14/19:

public class ZigzagIterator {
    /*
    * @param v1: A 1d vector
    * @param v2: A 1d vector
    */
    private Iterator<Integer> it1;
    private Iterator<Integer> it2;
    private int count = 0;
    public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
        // do intialization if necessary
        it1 = v1.iterator();
        it2 = v2.iterator();
        count = 0;
    }

    /*
     * @return: An integer
     */
    public int next() {
        int ans = 0;
        // write your code here
        if (!it1.hasNext()) {
            ans = (Integer)it2.next();
        } else if (!it2.hasNext()) {
            ans = (Integer)it1.next();
        } else if (count == 0) {
            ans = (Integer) it1.next();
            count = 1;
        } else {
            ans = (Integer) it2.next();
            count = 0;
        }

        return ans;
    }

    /*
     * @return: True if has next
     */
    public boolean hasNext() {
        // write your code here
        return it1.hasNext() || it2.hasNext();
    }
}

/**
 * Your ZigzagIterator object will be instantiated and called as such:
 * ZigzagIterator solution = new ZigzagIterator(v1, v2);
 * while (solution.hasNext()) result.add(solution.next());
 * Output result
 */