Assign the Minimum Number of Cars to Rental Requests
Quick Overview
Assign rental requests to the fewest cars using start-time sorting and an availability heap. Prove optimality through simultaneous overlap and explain why multiple minimum assignments are valid.
Assign the Minimum Number of Cars to Rental Requests
Company: Google
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
Each rental request has a unique request ID, a start time, and an end time. Assign a car ID to every request so that one car is never used by overlapping rentals, and return the minimum number of cars required along with a valid assignment.
### Constraints and Clarifications
Clarify whether a car ending a rental at time t can begin another at t. For this practice solution, use half-open intervals [start,end) with start<end, so immediate reuse is allowed. These endpoint and nonzero-duration choices are not specified in the report. No size bounds are supplied. Preserve request IDs when returning assignments. Car IDs are labels; several different minimum-car assignments can be valid, and no unique labeling or partition is required.
### What a Strong Answer Covers
Sort requests, reuse the earliest available car with a min-heap, retain the assignment, and prove that every newly allocated car is necessary. Explain how the endpoint convention changes the reuse comparison.
### Follow-up Questions
- What changes if touching intervals are considered overlapping?
- Why does sorting by request ID not generally support the greedy argument?
Overview: Assign rental requests to the fewest cars using start-time sorting and an availability heap. Prove optimality through simultaneous overlap and explain why multiple minimum assignments are valid.
Each rental request has a unique request ID, a start time, and an end time. Assign a car ID to every request so that one car is never used by overlapping rentals, and return the minimum number of cars required along with a valid assignment.
Constraints and Clarifications
Clarify whether a car ending a rental at time t can begin another at t. For this practice solution, use half-open intervals [start,end) with start<end, so immediate reuse is allowed. These endpoint and nonzero-duration choices are not specified in the report. No size bounds are supplied. Preserve request IDs when returning assignments. Car IDs are labels; several different minimum-car assignments can be valid, and no unique labeling or partition is required.
What a Strong Answer Covers Guidance
Sort requests, reuse the earliest available car with a min-heap, retain the assignment, and prove that every newly allocated car is necessary. Explain how the endpoint convention changes the reuse comparison.
Follow-up Questions Guidance
What changes if touching intervals are considered overlapping?
Why does sorting by request ID not generally support the greedy argument?