Recently interviewed with Agoda for Staff Software Engineer role. Could not clear the system design/platform round. Sharing the questions and discussion topics for others preparing for senior backend/platform roles.

Round 1 — Coding Round (60 mins)

Question 1 — Simple Chemical Formula Evaluation

Write a function:

calculateWeight(String formula)

Requirements:

• Supported elements:

  • C → 12
  • H → 1
  • O → 8

• No parentheses

• Single-digit multipliers only

Example:

Input:
CH4

Output:
16

Explanation:
C = 12
H4 = 1 × 4 = 4
Total = 16

Question 2 — Complex Chemical Formula Evaluation

Enhancement over previous problem:

• Nested parentheses supported
• Multipliers after parentheses apply to entire group

Examples:

Input:
H(CH4)2

Output:
33

Input:
((CH4))

Output:
16

Main concepts:

• Stack
• Parsing
• Recursive/group evaluation

Round 2 — Platform/System Design Round (60 mins)

Architecture Problem

Scenario:
A booking platform needs to expose APIs for external suppliers to fetch booking information.

Requirements:

• Support 10–20 suppliers

• Suppliers fetch bookings using different filters:

  • last 5 minutes
  • last 2 hours
  • last 1 day
  • next 7 days check-ins
  • next 30 days check-ins

• Peak traffic:

  • ~100 requests/minute

Existing proposal from team:

• External Booking API calls internal Booking API
• New endpoint fetches bookings by supplier ID and date range

Main discussion areas:

• Why external APIs should not directly hit core booking service
• Read replicas vs OLTP DB
• CDC/event streaming
• Pagination and cursor-based APIs
• Incremental sync tokens
• Rate limiting/throttling
• Caching strategy
• Security/authentication
• Supplier isolation

Architecture topics interviewer focused on:

• Scalability
• Loose coupling
• External API design
• Data synchronization
• Production readiness

Code Review Discussion

Second part of round involved reviewing Java code for supplier booking query API.

Focus areas:

• Clean code principles
• Single Responsibility Principle
• Dependency Injection
• Removing duplicate cache logic
• Enum-based behavior encapsulation
• Validation cleanup
• Exception handling
• Logging practices
• Cache key design
• Separation of mapper responsibilities

Interview was heavily focused on:

• Backend architecture thinking
• Maintainability
• Real-world production systems
• Senior/staff-level engineering judgment

Hope this helps others preparing for Agoda platform/backend interviews.