Design a time-versioned key-value store and find common free time

You are given two coding tasks.

Task 1: Time-versioned key-value store

Design an in-memory data structure that supports:

• set(key, value, timestamp) : store the string value for string key at integer timestamp .
• get(key, timestamp) -> value : return the value associated with key at the largest stored timestamp t such that t <= timestamp . If there is no such timestamp (or key was never set), return an empty string.

Notes / assumptions

• Multiple set operations may occur for the same key at different timestamps.
• Timestamps are integers; you may assume set calls for a given key arrive in non-decreasing timestamp order unless stated otherwise.

Task 2: Find time slots when everyone is available

You are given schedules for N people. Each person’s schedule is a list of busy time intervals during the day.

• Each busy interval is [start, end) with start < end .
• For each person, their busy intervals are non-overlapping and sorted by start time.

Return all time intervals (also as [start, end)) when everyone is available (i.e., when no one is busy). Only include intervals with positive length.

Clarify in your solution

• What overall day bounds apply (e.g., [0, 24*60) minutes) and how to handle availability outside provided busy intervals.

Input / Output format (for Task 2)

• Input: schedules: List[List[Interval]] , where schedules[i] is person i ’s busy intervals.
• Output: List[Interval] representing common free time intervals.