"""

Zigzag Iterator

Interleave elements from two lists in a zigzag fashion. Elements are

yielded alternately from each list until both are exhausted.

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

Complexity:

Time: O(n) total across all next() calls

Space: O(n)

"""

from __future__ import annotations

class ZigZagIterator:

"""Iterator that interleaves elements from two lists.

Examples:

>>> it = ZigZagIterator([1, 2], [3, 4, 5])

>>> it.next()

1

>>> it.next()

3

"""

def __init__(self, v1: list[int], v2: list[int]) -> None:

"""Initialize with two lists.

Args:

v1: First input list.

v2: Second input list.

"""

self.queue: list[list[int]] = [lst for lst in (v1, v2) if lst]

def next(self) -> int:

"""Return the next element in zigzag order.

Returns:

The next interleaved element.

"""

current_list = self.queue.pop(0)

ret = current_list.pop(0)

if current_list:

self.queue.append(current_list)

return ret

def has_next(self) -> bool:

"""Check if there are more elements.

Returns:

True if elements remain, False otherwise.

"""

return bool(self.queue)