HackTheRounds Interview Experiences

Microsoft L62 Software Engineer Interview Experience (2026) - Coding, LLD & HLD, Offer

A four round Microsoft L62 loop featuring an expression evaluator, library low level design, e commerce system design, and a managerial round.

By HackTheRounds Team · 2026-07-01

Background

My Microsoft L62 loop took place over two days in July 2026. It consisted of four interviews of roughly 45 minutes each: coding, low-level design, high-level design, and a managerial round. I made an imperfect first attempt in nearly every technical round, but the interviewers used follow-up questions to see whether I could identify the flaw and repair the design.

That became the defining pattern of the loop. A correct first answer helped, but responding well to a constraint or counterexample mattered just as much.

Round 1: Coding - Expression Evaluator

Problem: Parse and evaluate an arithmetic expression containing addition, subtraction, multiplication, division, parentheses, whitespace, multi-digit integers, and unary signs. Normal precedence must be preserved.

My first idea was a left-to-right scan. A tiny counterexample—addition followed by multiplication—showed immediately that it would produce the wrong result. I restarted with a recursive-descent structure:

The factor layer was the important correction. Treating every minus sign as a binary operator failed when an expression began with a negative number or contained consecutive signs. Making unary signs part of factor parsing fixed both cases without scattering special conditions through the rest of the parser.

Follow-ups covered malformed parentheses, division by zero, integer overflow, complexity, and adding exponentiation. I described a full-input validation pass, long intermediate values, and a new right-associative precedence layer for exponentiation. Time was linear in the input length, with stack depth proportional to parenthesis nesting.

Round 2: Low-Level Design - Library Management

Problem: Design a library system that supports members, books, borrowing, returns, and future extensions.

I initially modeled a book with one isAvailable flag. The interviewer asked what happens when a library owns three physical copies of the same title. That exposed the modeling error: a bibliographic work and a lendable item are different entities.

I split the design into Book for ISBN-level metadata and BookItem for a specific barcoded copy with its own status. A Loan connected one copy to one member and tracked relevant dates. Borrowing selected an available copy rather than changing shared title state.

Follow-ups included a reservation queue, concurrent attempts to borrow the final copy, lost items, loan limits, and digital editions. I proposed a per-title hold queue, an atomic availability transition, an explicit lost state, and an interface that could support physical and digital items without rewriting the circulation workflow.

Round 3: High-Level Design - E-Commerce Shopping

The system needed product search and filtering, product details, secure checkout, and integration with an existing inventory service. The prompt supplied a catalog of about ten million products, one million daily users, and a much smaller but correctness-sensitive order stream.

My first diagram put every workload in one relational database. The interviewer challenged full-text search across the catalog, and I separated storage by access pattern:

  • A search index served keyword queries, filters, and sorting.
  • A catalog store plus cache served product details.
  • A strongly consistent relational store owned orders and payments.
  • A queue decoupled downstream inventory work where the user-facing path did not require synchronous completion.

The next challenge was overselling the last unit. A read-then-write decrement allows two checkouts to observe the same stock. I corrected the design with a conditional update or version check and added idempotency keys so a network retry would not create a duplicate order.

We also discussed traffic spikes, search-index sharding, cache scaling, and reconciliation when asynchronous inventory updates fail. I emphasized that average traffic is not capacity planning; promotions create peaks, and correctness paths need explicit failure handling.

Round 4: Managerial and Behavioral

The final round focused on resume ownership, conflict, ambiguity, and learning from mistakes, with a short design follow-up. The interviewer repeatedly separated my actions from the team's actions. General statements about collaboration were less useful than one decision, the evidence behind it, and the measurable result.

I used specific stories and included what I would change. That made the discussion feel less like defending a flawless record and more like demonstrating judgment.

Result

I was selected for the L62 software engineer role. The offer was encouraging, but the more reusable lesson was that recovery is part of the evaluation. In three rounds, a counterexample invalidated my first simplification. Saying so clearly and rebuilding from the requirement was stronger than trying to defend it.

Tips

  1. Test your idea with the smallest counterexample before you commit to implementation.
  2. In parsing problems, define the grammar and precedence layers out loud.
  3. In LLD, separate a conceptual entity from its individual inventory instances.
  4. In system design, choose stores by access pattern and consistency needs, not familiarity.
  5. Make concurrency concrete: name the atomic transition, version check, lock, or idempotency key.
  6. Prepare behavioral stories that distinguish your own judgment from the team's outcome.