0281. Zigzag Iterator

https://leetcode.com/problems/zigzag-iterator

Description

Given two vectors of integers v1 and v2, implement an iterator to return their elements alternately.

Implement the ZigzagIterator class:

• ZigzagIterator(List<int> v1, List<int> v2) initializes the object with the two vectors v1 and v2.

• boolean hasNext() returns true if the iterator still has elements, and false otherwise.

• int next() returns the current element of the iterator and moves the iterator to the next element.

Example 1:

**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].

Example 2:

**Input:** v1 = [1], v2 = []
**Output:** [1]

Example 3:

**Input:** v1 = [], v2 = [1]
**Output:** [1]

Constraints:

• 0 <= v1.length, v2.length <= 1000

• 1 <= v1.length + v2.length <= 2000

• -231 <= v1[i], v2[i] <= 231 - 1

Follow up: What if you are given k 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".

Example:

**Input:** v1 = [1,2,3], v2 = [4,5,6,7], v3 = [8,9]
**Output:** [1,4,8,2,5,9,3,6,7]

ac

public class ZigzagIterator {
    private Queue<int[]> q;
    private List<List<Integer>> lists;

    public ZigzagIterator(List<Integer> v1, List<Integer> v2) {
        lists = new ArrayList<List<Integer>>();
        lists.add(v1);
        lists.add(v2);

        q = new LinkedList<int[]>();
        if (v1.size() > 0) q.offer(new int[] {0, 0});
        if (v2.size() > 0) q.offer(new int[] {1, 0});
    }

    public int next() {
        int[] head = q.poll();
        int res = lists.get(head[0]).get(head[1]);
        if (++head[1] < lists.get(head[0]).size()) q.offer(head);
        return res;
    }

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

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