Zigzag Iterator 解答

Question

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?

Solution

This solution is suitable for k vectors.

public class ZigzagIterator {
    private List<Iterator> list;

    public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
        list = new ArrayList<Iterator>();
        if (v1.iterator().hasNext())
            list.add(v1.iterator());
        if (v2.iterator().hasNext())
            list.add(v2.iterator());
    }

    public int next() {
        Iterator<Integer> current = list.remove(0);
        int result = current.next();
        if(current.hasNext())
            list.add(current);
        return result;        
    }

    public boolean hasNext() {
        return list.size() > 0 ? true : false;
    }
}

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