Find available reservation time slots
Company: Pinterest
Role: Data Scientist
Category: Coding & Algorithms
Difficulty: Medium
Interview Round: Onsite
## Problem
You are building an API to show which time slots are available for booking at a restaurant.
You are given:
- The restaurant’s **opening hours** (per day), and
- A list of **existing reservations** (per day), each with a start and end time.
Opening hours and reservations are provided in a **nested dictionary** structure.
### Input
Assume times are in the same timezone and represented as minutes-from-midnight or as `HH:MM` strings that can be converted to minutes.
- `hours[day] = [open_time, close_time]`
- `reservations[day] = [[start1, end1], [start2, end2], ...]`
Example shape:
```python
hours = {
"Mon": ["11:00", "22:00"],
"Tue": ["11:00", "22:00"],
}
reservations = {
"Mon": [["12:00", "12:30"], ["18:00", "19:15"]],
"Tue": [],
}
```
### Task
Write a function that returns, for each day, the list of **available time intervals** within opening hours that are not blocked by existing reservations.
Clarify/handle these cases:
- Reservations may be unsorted.
- Reservations may touch endpoints (e.g., one ends at 13:00 and another starts at 13:00).
- If reservations overlap, they should be merged before computing availability.
### Output
Return a nested dictionary:
- `available[day] = [[free_start1, free_end1], [free_start2, free_end2], ...]`
(Optionally, if a booking duration `D` minutes is provided, return only free intervals of length `>= D`, or return discrete start times valid for a `D`-minute reservation—state your choice.)
Quick Answer: This question evaluates a candidate's ability to reason about time-interval data and temporal normalization, testing competencies in interval manipulation, conflict detection, and algorithmic problem-solving for scheduling contexts.