Zigzag Iterator

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

Have you met this question in a real interview? 

Yes

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].

這個迭代器必須要是用if else if這種結構，否則將出現錯誤

java

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

    /*
     * @return: An integer
     */
    public int next() {
        // write your code here
        int val = 0;
        if ((flag && it1.hasNext()) || !it2.hasNext()) {
            val = it1.next();
        } else if ((!flag && it2.hasNext()) || !it1.hasNext()) {
            val = it2.next();
        }
        return val;
    }

    /*
     * @return: True if has next
     */
    public boolean hasNext() {
        // write your code here
        flag = !flag;
        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
 */