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".

Follow-up Example:

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