Find the Closest Version by Date

Problem Statement

You are working on a document versioning system at Amazon. You are given a list of Version objects, where each object contains a version_id (a string) and a created_at (a Unix timestamp). The list is sorted by created_at in ascending order.

Implement a function find_closest_version(versions, target_date) that returns the version_id of the version that was active or closest to the target_date. If two versions are equally close to the target_date, return the one with the earlier created_at timestamp. If the target_date is earlier than any existing version, return the version_id of the earliest version.

Function Signature

class Version:
    def __init__(self, version_id, created_at):
        self.version_id = version_id
        self.created_at = created_at

def find_closest_version(versions: list[Version], target_date: int) -> str:
    pass

Constraints

• 1 <= len(versions) <= 10^5
• 0 <= created_at, target_date <= 10^12
• The versions list is pre-sorted by created_at.

Examples

Example 1:

• versions = [Version('v1', 100), Version('v2', 200), Version('v3', 300)]
• target_date = 250
• Output: 'v2' (200 is closer to 250 than 300 is, or equally spaced, we return the earlier one if needed, but here 200 is clearly closer).

Example 2:

• versions = [Version('a', 10), Version('b', 20)]
• target_date = 5
• Output: 'a' (Target is before the first version).

Edge Cases

• The target_date is exactly equal to one of the created_at timestamps.
• The target_date is larger than any timestamp in the list.
• The list contains only one version.