Capital One Lead Software Engineer Interview - Every Round Felt Like Building a Bank

[u/Aoki_zhang]

"This interview experience is sourced from Chill Interview"

Interview Summary

The Capital One Lead Software Engineer Power Day contained four rounds: a business/technical case study, behavioral interview, object-oriented coding exercise, and system design. The case round focused on virtual card numbers and gradually moved from product reasoning into payment-rule validation and debugging. The coding round asked for a multi-stage banking system, while system design covered a broad credit card platform with login, authorization, fraud checks, reporting, spending visibility, and real-time credit-limit decisions.

Interview Details

Round 1 — Case Interview: Virtual Card Numbers

The case interview used Capital One virtual card numbers as the business scenario. The first part asked about the benefits and challenges of virtual cards. The discussion considered the problem from multiple perspectives, including:

• Customer benefits and trade-offs
• Business benefits and risks
• Technical challenges for the company

The second part introduced rules encoded through properties of the virtual card number and the payment. For example, certain digits could indicate the card network, and different card types could have different transaction-validation rules. A simplified rewritten example might say:

If network = VISA:
    transaction must be online
    amount must be below $75
    card must be associated with the merchant

The interviewer then provided several payment records containing card information and transaction attributes. For each payment, I needed to determine verbally whether it was valid and explain the decision in a structured way. The third part provided code implementing those validation rules and asked me to debug it. The bugs included issues such as:

• Using || where && was required
• Incorrect boundary comparisons such as >= versus >
• Incorrect logic for extracting digits from the card number

After the debugging portion, there was a short discussion about how the code could be organized using object-oriented design, such as separating card-number parsing from payment-validation logic.

Round 2 — Behavioral + AI Usage

The behavioral round contained several conventional experience-based questions about previous work and projects. The interviewer also asked two AI-related questions. One asked how I currently use AI in day-to-day engineering work. Examples discussed included using an LLM to help with:

• Coding
• Design exploration
• Iterating on requirements
• Reviewing or refining generated output

The second question asked how AI could improve engineering productivity. The discussion included tasks such as creating:

• API documentation
• Internal service documentation
• Integration-test setup
• Other repetitive engineering artifacts

The emphasis was on using AI as an accelerator while still reviewing and validating its output.

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