## 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]`.```

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]`.
```

## Rust Solution

``````use std::collections::VecDeque;
use std::iter::FromIterator;

#[derive(Debug)]
struct ZigzagIterator {
queues: VecDeque<VecDeque<i32>>,
}

impl<'a> ZigzagIterator {
fn new(v1: Vec<i32>, v2: Vec<i32>) -> Self {
let mut queues = VecDeque::new();
if !v1.is_empty() {
queues.push_back(VecDeque::from_iter(v1));
}
if !v2.is_empty() {
queues.push_back(VecDeque::from_iter(v2));
}
ZigzagIterator { queues }
}

fn next(&mut self) -> i32 {
let mut first = self.queues.pop_front().unwrap();
let res = first.pop_front().unwrap();
if !first.is_empty() {
self.queues.push_back(first);
}
res
}

fn has_next(&self) -> bool {
!self.queues.is_empty()
}
}

#[test]
fn test() {
let v1 = vec![1, 2];
let v2 = vec![3, 4, 5, 6];
let res = vec![1, 3, 2, 4, 5, 6];
let mut obj = ZigzagIterator::new(v1, v2);
let mut ans = vec![];
while obj.has_next() {
ans.push(obj.next());
}
assert_eq!(ans, res);
}
``````

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