Delivery agent assignment in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Key factors in delivery agent assignment

Which factor is the most critical to consider when assigning a delivery agent to a new order to ensure timely delivery?

A The delivery agent's shoe size

B The delivery agent's favorite food preferences

C The color of the delivery agent's vehicle

D The delivery agent's current location relative to the pickup point

💡 Hint

Think about what affects how fast the agent can reach the pickup location.

The delivery agent's current location is crucial because it directly impacts how quickly they can reach the pickup point and start the delivery.

❓ Architecture

intermediate

Component responsible for agent assignment

In a delivery system architecture, which component should handle the logic for assigning delivery agents to orders?

A Delivery Assignment Service

B User Interface Layer

C Database Storage Engine

D Payment Processing Module

💡 Hint

Consider which part of the system makes decisions about who does what.

The Delivery Assignment Service is designed to handle the logic of matching orders with available delivery agents based on various factors.

❓ scaling

advanced

Scaling delivery agent assignment for peak hours

What is the best approach to scale the delivery agent assignment system during peak order times to maintain performance?

A Implement a distributed queue system to handle assignment requests asynchronously

B Increase the font size on the delivery app interface

C Reduce the number of delivery agents available

D Disable the assignment system temporarily

💡 Hint

Think about how to handle many requests efficiently without blocking.

A distributed queue system allows the assignment requests to be processed asynchronously and in parallel, improving scalability and responsiveness during peak times.

❓ tradeoff

advanced

Tradeoff between assignment speed and accuracy

Choosing between a fast but less accurate delivery agent assignment and a slower but more accurate one, what is a key tradeoff to consider?

A Slower assignment always leads to better customer satisfaction

B Accuracy does not affect delivery times or customer experience

C Faster assignment may reduce delivery quality but improve customer wait times

D Speed and accuracy are unrelated in delivery systems

💡 Hint

Think about how speed and quality affect customer experience differently.

Faster assignment can reduce wait times but might assign less optimal agents, affecting delivery quality. Slower assignment may improve match quality but increase wait times.

❓ estimation

expert

Estimating system capacity for delivery agent assignment

If a city has 10,000 active delivery agents and each agent can handle 3 deliveries per hour, what is the maximum number of orders the assignment system should support per hour without delays?

A 13,000 orders per hour

B 30,000 orders per hour

C 3,000 orders per hour

D 10,000 orders per hour

💡 Hint

Multiply the number of agents by deliveries per agent per hour.

10,000 agents × 3 deliveries each = 30,000 orders per hour capacity without delays.

Practice

1.

What is the primary goal of a delivery agent assignment system?

easy

A. Match orders to available delivery agents nearby

B. Track payment details of customers

C. Manage inventory in warehouses

D. Calculate delivery charges for orders

Solution

1. Step 1: Understand the system purpose

   The delivery agent assignment system focuses on connecting orders with delivery agents who can fulfill them.

2. Step 2: Identify the main function

   Matching orders to free agents nearby ensures timely delivery and efficient resource use.

3. Final Answer:

   Match orders to available delivery agents nearby -> Option A

4. Quick Check:

   Delivery agent assignment = Matching orders to agents [OK]

Hint: Focus on matching orders to agents, not payments or inventory [OK]

Common Mistakes:

• Confusing delivery assignment with payment processing
• Thinking inventory management is part of agent assignment
• Assuming delivery charges calculation is the main goal

2.

Which data structure is best to quickly find the nearest free delivery agent for an order?

easy

A. Priority queue sorted by distance from order location

B. Stack of agents in order of registration

C. Hash map keyed by agent ID

D. Linked list of all agents

Solution

1. Step 1: Identify the need for sorting by distance

   To find the nearest free agent, sorting agents by their distance to the order location is essential.

2. Step 2: Choose a data structure supporting efficient nearest retrieval

   A priority queue can efficiently provide the closest agent by always giving the smallest distance first.

3. Final Answer:

   Priority queue sorted by distance from order location -> Option A

4. Quick Check:

   Nearest agent search = Priority queue [OK]

Hint: Use priority queue for nearest-first retrieval [OK]

Common Mistakes:

• Using hash map which doesn't sort by distance
• Using stack or linked list which are inefficient for nearest search
• Ignoring the need to sort by distance

3.

Consider this pseudocode for assigning an agent:
for agent in agents:
  if agent.status == 'free' and distance(agent, order) < min_distance:
    min_distance = distance(agent, order)
    assigned_agent = agent
return assigned_agent
What will this code return if all agents are busy?

medium

A. The closest free agent

B. None or null

C. The first agent in the list

D. An error due to undefined variable

Solution

1. Step 1: Check variable initializations

   The code does not initialize assigned_agent or min_distance before the loop.

2. Step 2: Trace execution when all agents are busy

   The if condition's first part (agent.status == 'free') fails for all agents, so due to short-circuit evaluation of 'and', the second part (distance < min_distance) is never evaluated. The loop ends without ever setting assigned_agent. Returning an uninitialized assigned_agent causes an error due to undefined variable.

3. Final Answer:

   An error due to undefined variable -> Option D

4. Quick Check:

   No initialization + all busy = undefined variable error [OK]

Hint: No variable initialization leads to undefined variable error [OK]

Common Mistakes:

• Thinking assigned_agent defaults to None or null
• Assuming it returns the first agent regardless of status
• Believing the code handles no free agents gracefully

4.

Given this snippet:
assigned_agent = None
for agent in agents:
  if agent.status = 'free':
    assigned_agent = agent
return assigned_agent
What is the main error in this code?

medium

A. Returning assigned_agent inside the loop

B. Not initializing assigned_agent before loop

C. Using assignment operator '=' instead of comparison '==' in if condition

D. Using 'free' instead of 'available' as status

Solution

1. Step 1: Check the if condition syntax

   The condition uses '=' which assigns value instead of '==' which compares values.

2. Step 2: Understand impact of wrong operator

   This causes a syntax error or unintended behavior because '=' cannot be used in conditions.

3. Final Answer:

   Using assignment operator '=' instead of comparison '==' in if condition -> Option C

4. Quick Check:

   Use '==' for comparison, not '=' [OK]

Hint: Use '==' for comparisons in conditions [OK]

Common Mistakes:

• Confusing '=' with '==' in if statements
• Thinking assigned_agent must be initialized inside loop
• Assuming return inside loop is the error

5.

You want to design a scalable delivery agent assignment system for a city with thousands of agents and orders per minute. Which approach best improves scalability?

hard

A. Use a centralized server to check all agents for every order

B. Partition the city into zones and assign agents within zones only

C. Assign agents randomly without considering location

D. Assign the oldest registered agent to every order

Solution

1. Step 1: Understand scalability challenges

   Checking all agents for every order is slow and resource-heavy at large scale.

2. Step 2: Choose a partitioning strategy

   Dividing the city into zones limits search space, making assignment faster and scalable.

3. Step 3: Evaluate other options

   Random or oldest agent assignment ignores location, causing delays and inefficiency.

4. Final Answer:

   Partition the city into zones and assign agents within zones only -> Option B

5. Quick Check:

   Zone partitioning = scalable assignment [OK]

Hint: Divide city into zones to limit search scope [OK]

Common Mistakes:

• Using centralized server causing bottlenecks
• Ignoring agent location in assignment
• Assigning agents randomly or by registration time