Mock Scenario Test: Rave Developer Assessment

Many airlines will issue a take-home assignment or live coding test to evaluate your declarative logic skills. Since standard platforms like LeetCode do not support Rave, they will usually ask you to write pseudo-Rave code or evaluate a logic puzzle.

Here is a realistic mock scenario.

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📌 The Scenario

Background: You are optimizing schedules for a European base. The union CBA states that a crew member's total flight time in a single Duty cannot exceed 9 hours (09:00). Additionally, the union strongly prefers that crews do not sit on the ground between flights for more than 2 hours (02:00).

The Requirements:

1. Write a hard constraint to ensure the total flight time in a duty does not exceed 09:00.
2. Write a soft penalty that adds 50.0 cost points for every minute of sit time that exceeds 02:00 between any two consecutive flights in a duty.
3. Add this penalty to the total cost of the Duty.

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💻 Your Task

Write the Rave code to implement these requirements.

Hint: Remember how to use monotonic constraints, the sum traverser, and the for each inter-instance navigator.

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✅ Solution & Explanation

Part 1: The Hard Constraint (Flight Time Limit)

This is a classic monotonic limit. We want this to be a Final Rule so it prunes the search space efficiently.

CONSTANTS:
  %max_flight_time% = 09:00;
ENDCONSTANTS

// The compiler will infer this as a Final Rule because flight time is non-negative
CONSTRAINT max_duty_flight_time OF Duty
  COMMENT: "Total flight time in a duty must not exceed 9 hours."
  STATUS: ON;
  RULE:
    sum(leg(duty), leg.%flight_time%) <= %max_flight_time%;
ENDCONSTRAINT

Part 2: The Sit Time Soft Penalty

We need to iterate over consecutive legs, check the sit time, and calculate a penalty if it exceeds 2 hours.

CONSTANTS:
  %max_sit_time_threshold% = 02:00;
  %sit_time_penalty_per_min% = 50.0;
ENDCONSTANTS

// Calculate the penalty for a single connection
%connection_sit_penalty% = 
  for each f1 -> f2 in elements
    if (f2.departure_time - f1.arrival_time) > %max_sit_time_threshold% then
      // Convert the excess duration to minutes and multiply by the penalty weight
      ((f2.departure_time - f1.arrival_time) - %max_sit_time_threshold%) * %sit_time_penalty_per_min%
    else
      0.0;

// Aggregate the penalties across the entire duty
%total_duty_sit_penalty% = sum(leg(duty), %connection_sit_penalty%);

Part 3: The Duty Cost Property

Finally, we add this penalty to the base cost of the duty.

PROPERTY cost OF Duty
  RULE:
    %base_duty_cost% + %total_duty_sit_penalty%;
ENDPROPERTY

🧠 Interviewer Follow-Up Question:

• Interviewer: "Why didn't you put valid is_closed; inside the max_duty_flight_time constraint?"
• Your Response: "Because total flight time is a non-decreasing monotonic sum. By leaving valid is_closed; out, the compiler correctly identifies it as a Final Rule. If I added is_closed, it would turn into an Illegal Subchain Rule, the solver would stop pruning the tree early, and performance would plummet."