Debug and harden a driver-selection component

Debugging Exercise: “Pick Dasher”

You are given a small codebase for selecting a dasher (driver) using a heap/priority-queue–like structure.

The current implementation is failing tests / behaving incorrectly. While debugging, you notice issues such as:

• A required constructor was not implemented/initialized properly.
• A method similar to adjustKey() has an off-by-one bug: it uses something like size - 1 when size is already the correct last index (or vice versa).

Tasks

1. Identify and fix the bug(s) so the selection logic works correctly.
2. Write your own test cases that reproduce the failure and verify the fix.

Follow-up (production readiness)

If this were production code, what changes would you make beyond the minimal bug fix? Consider:

• input validation
• error handling
• logging/metrics
• performance
• maintainability (API design, naming, invariants, documentation)
• test strategy (unit/integration/property-based)
• rollout safety (feature flags, canary)