281. Zigzag Iterator

281. Zigzag Iterator

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

Example:

Input:
v1 = [1,2]
v2 = [3,4,5,6] 

Output: [1,3,2,4,5,6]

Explanation: 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:
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:

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

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

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Solution #1, 通用方法

public class ZigzagIterator {

    private boolean v1True = true;
    private List<Integer> v1;
    private List<Integer> v2;
    private int i1;
    private int i2;
    
    public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
        this.v1 = v1;
        this.v2 = v2;
        i1 = 0;
        i2 = 0;
    }

    public int next() {
        int rt;
        if (v1True) {
            if (i1 < v1.size()) {
                rt = v1.get(i1);
                i1++;
                v1True = false;
            }else {
                rt = v2.get(i2);
                i2++;
            }
        } else {
            if (i2 < v2.size()) {
                rt = v2.get(i2);
                i2++;
                v1True = true;
            }else {
                rt = v1.get(i1);
                i1++;
            }
        }
        
        return rt;
    }

    public boolean hasNext() {
        return i1 < v1.size() || i2 < 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();
 */

Solution #2, Java Iterator

public class ZigzagIterator {

    private Queue<Iterator> que;
    private List<Integer> v1;
    private List<Integer> v2;
    
    public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
        que = new LinkedList<Iterator>();
        this.v1 = v1;
        this.v2 = v2;
        if (!v1.isEmpty()) que.add(v1.iterator());
        if (!v2.isEmpty()) que.add(v2.iterator());
    }

    public int next() {
        
        Iterator i = que.poll();
        int next = (Integer)i.next();
        
        if (i.hasNext()) que.add(i);
        
        return next;
    }

    public boolean hasNext() {
        return !que.isEmpty();
    }
}

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