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.

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Google
Jun 27, 2026
mediumSoftware EngineerTechnical ScreenCoding & Algorithms
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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?