Delivery agent assignment in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to assign a delivery agent to an order.

LLD

order.assignAgent([1])

Drag options to blanks, or click blank then click option'

Aorder

Bagent

Cdelivery

Dassign

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the order object instead of the agent.

Using a method name instead of an object.

The assignAgent method requires the delivery agent object to assign it to the order.

2fill in blank

medium

Complete the code to check if the delivery agent is available before assignment.

LLD

if (agent.[1]()) {
    order.assignAgent(agent);
}

Drag options to blanks, or click blank then click option'

AisBusy

Bdeliver

Cassign

DisAvailable

Attempts:

3 left

💡 Hint

Common Mistakes

Using isBusy() which returns the opposite.

Calling a method that does not exist.

The isAvailable() method checks if the agent is free to take a new delivery.

3fill in blank

hard

Fix the error in the code to update the agent's status after assignment.

LLD

agent.[1] = false;

Drag options to blanks, or click blank then click option'

AassignAgent

BisAvailable

Cavailable

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name instead of a property.

Setting the wrong property.

The available property should be set to false to mark the agent as busy.

4fill in blank

hard

Fill both blanks to create a function that assigns the first available agent from a list.

LLD

function assignFirstAvailableAgent(order, agents) {
    for (let [1] of agents) {
        if ([2].isAvailable()) {
            order.assignAgent([2]);
            break;
        }
    }
}

Drag options to blanks, or click blank then click option'

Aagent

Border

Dagents

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inside the loop.

Using the order or agents list as the loop variable.

The loop variable should be agent to represent each delivery agent in the list. The same variable is used to check availability and assign.

5fill in blank

hard

Fill all three blanks to implement a method that returns a list of available agents.

LLD

function getAvailableAgents([1]) {
    return [2].filter([3] => [3].isAvailable());
}

Drag options to blanks, or click blank then click option'

Aagents

Cagent

Dorder

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the parameter and the array.

Using a variable name that conflicts with the parameter.

The parameter and the array to filter are both agents. The filter callback uses agent as the variable representing each element.

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