Split strategies (equal, exact, percentage) in LLD - Architecture Diagram

System Overview - Split strategies (equal, exact, percentage)

This system manages how a total amount is divided among multiple recipients using different split strategies: equal, exact, and percentage. It ensures accurate distribution based on user input and handles validations to prevent errors.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  v
Split Service
  |       |        |
  v       v        v
Equal   Exact   Percentage
Handler Handler Handler
  |       |        |
  v       v        v
Database (Split Records)
  |
  v
Cache (Recent Splits)

Components

User

client

Initiates split requests with chosen strategy and amounts

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway instances

API Gateway

api_gateway

Routes requests to the Split Service and handles authentication

Split Service

service

Processes split requests and delegates to specific strategy handlers

Equal Handler

service_component

Calculates equal splits among recipients

Exact Handler

service_component

Processes splits with exact amounts per recipient

Percentage Handler

service_component

Calculates splits based on percentage values per recipient

Database (Split Records)

database

Stores split transaction records and user data

Cache (Recent Splits)

cache

Caches recent split results for faster retrieval

Request Flow - 11 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Split Service

Split Service → Cache (Recent Splits)

Cache (Recent Splits) → Split Service

Split Service → Equal Handler / Exact Handler / Percentage Handler

Equal Handler / Exact Handler / Percentage Handler → Split Service

Split Service → Database (Split Records)

Split Service → Cache (Recent Splits)

Split Service → API Gateway

API Gateway → User

Failure Scenario

Component Fails:Database (Split Records)

Impact:New split transactions cannot be saved, risking data loss; reads may fallback to cache but may be stale

Mitigation:Use database replication and failover; cache serves recent splits temporarily; alert system triggers for manual intervention

Architecture Quiz - 3 Questions

Which component is responsible for deciding how to split the amount based on the strategy?

A API Gateway

B Split Service

C Load Balancer

D Cache

Design Principle

This architecture cleanly separates concerns by using dedicated handlers for each split strategy, enabling easy extension and maintenance. Caching improves performance by avoiding repeated calculations, and the use of load balancer and API gateway ensures scalability and security.

Practice

1. Which split strategy divides an amount so that everyone pays the same share regardless of individual preferences?

easy

A. Equal split

B. Exact split

C. Percentage split

D. Random split

Solution

1. Step 1: Understand the definition of equal split

   Equal split means dividing the total amount evenly among all participants.

2. Step 2: Compare with other splits

   Exact split assigns specific amounts, percentage split assigns based on percent, random split is not a standard method.

3. Final Answer:

   Equal split -> Option A

4. Quick Check:

   Equal split = same share for all [OK]

Hint: Equal split means everyone pays the same amount [OK]

Common Mistakes:

• Confusing exact split with equal split
• Thinking percentage split always equals equal split
• Assuming random split is a valid standard method

2. Which of the following is the correct syntax to represent a percentage split of 40% for user A and 60% for user B in a system design context?

easy

A. {'A': '40%', 'B': '60%'}

B. {'A': 40, 'B': 60}

C. {'A': 0.4, 'B': 0.6}

D. {'A': 4, 'B': 6}

Solution

1. Step 1: Understand percentage representation in decimals

   Percentages are often represented as decimals between 0 and 1 in code for calculations.

2. Step 2: Evaluate options

   {'A': 0.4, 'B': 0.6} uses decimals summing to 1, correct for percentage split. {'A': 40, 'B': 60} uses integers but not decimals. {'A': '40%', 'B': '60%'} uses strings which are not directly usable. {'A': 4, 'B': 6} uses incorrect smaller numbers.

3. Final Answer:

   {'A': 0.4, 'B': 0.6} -> Option C

4. Quick Check:

   Decimal form for percentages = {'A': 0.4, 'B': 0.6} [OK]

Hint: Use decimals (0.4) not integers (40) for percentage splits [OK]

Common Mistakes:

• Using integers instead of decimals for percentages
• Using strings with % symbol in code
• Not ensuring sum equals 1

3. Given a total amount of 100 and a split strategy: {'A': 30, 'B': 70} as exact amounts, what is the amount assigned to user B?

medium

A. 70

B. 100

C. 30

D. 0

Solution

1. Step 1: Identify the split type and amounts

   The split is exact, so amounts are assigned directly as given.

2. Step 2: Find user B's assigned amount

   User B is assigned 70 as per the exact split dictionary.

3. Final Answer:

   70 -> Option A

4. Quick Check:

   Exact split assigns given amounts = 70 [OK]

Hint: Exact split means use given amounts directly [OK]

Common Mistakes:

• Adding amounts instead of reading assigned value
• Confusing exact with percentage split
• Assuming equal split when exact is given

4. In a percentage split system, if the sum of percentages provided is 110%, what is the main issue and how should it be fixed?

medium

A. The sum is valid, no fix needed

B. The sum should be exactly 0%, reset all percentages

C. The sum is less than 100%, add missing percentage

D. The sum exceeds 100%, fix by normalizing percentages to sum to 100%

Solution

1. Step 1: Identify the problem with sum of percentages

   Percentages must sum to 100% (or 1 in decimal) to correctly split amounts.

2. Step 2: Determine the fix

   If sum is 110%, it exceeds total amount. Normalize by scaling percentages so they sum to 100%.

3. Final Answer:

   The sum exceeds 100%, fix by normalizing percentages to sum to 100% -> Option D

4. Quick Check:

   Sum > 100% requires normalization [OK]

Hint: Percentages must sum to 100%, else normalize [OK]

Common Mistakes:

• Ignoring sum validation
• Assuming sum can be more than 100%
• Trying to add missing percentage when sum is too high

5. You need to design a system that supports splitting a bill among users using equal, exact, or percentage strategies. Which approach best ensures scalability and correctness when handling thousands of users?

hard

A. Allow users to input any split without checks and calculate on demand

B. Use a unified split interface that validates input and applies the correct split logic per strategy

C. Store all splits as exact amounts without validation

D. Hardcode equal split only to simplify calculations

Solution

1. Step 1: Identify requirements for scalability and correctness

   System must handle many users and ensure splits are valid and consistent.

2. Step 2: Evaluate design approaches

   Unified interface with validation ensures correctness and flexibility. Hardcoding or no validation risks errors and poor scalability.

3. Final Answer:

   Use a unified split interface that validates input and applies the correct split logic per strategy -> Option B

4. Quick Check:

   Unified validated interface = scalable & correct [OK]

Hint: Validate splits and use unified logic for scalability [OK]

Common Mistakes:

• Ignoring validation leading to incorrect splits
• Hardcoding one strategy limits flexibility
• Allowing unchecked input causes errors at scale