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HashedIn by Deloitte Software Engineer Interview Guide

HashedIn by Deloitte Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

As a Software Engineer at HashedIn by Deloitte, you sit at the intersection of modern product engineering and enterprise-scale solution delivery. HashedIn by Deloitte specializes in building cloud-native SaaS solutions, enterprise digital platforms, and high-throughput data pipelines. In this role, you are responsible for designing, developing, and deploying robust software platforms that solve complex technical problems for global clients across diverse industries. The impact of a Software Engineer at HashedIn by Deloitte extends beyond simple feature delivery. You will engineer core services, optimize database architectures, and design resilient microservices capable of handling high transaction volumes.

This guide is scoped to a Software Engineer candidate at HashedIn by Deloitte.

Focus areas

  • Data Structures
  • Algorithms
  • Problem Solving (Approach & Thought Process)

The HashedIn by Deloitte interview process

HashedIn by Deloitte candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Online Assessment

Candidates must complete an online coding assessment that includes public and hidden test cases to advance.

What to demonstrate

  • Candidates must complete an online coding assessment that includes public and hidden test cases to advance
  • Depth in Data Structures

How to prepare

  • Answer aloud and timed: Given a string, find the length of the minimum window substring containing all required characters.
  • Answer aloud and timed: Decode an encoded string with nested repetition counts, such as expanding 3[a2[bc]] into abcbcabcbcabcbc.

Technical Round 1

Focus on Data Structures, Algorithms, and Core CS subjects, requiring candidates to write pseudocode or functional code.

What to demonstrate

  • Focus on Data Structures, Algorithms, and Core CS subjects, requiring candidates to write pseudocode or functional code
  • Depth in Data Structures

How to prepare

  • Answer aloud and timed: Given an array of integers, find the continuous subarray whose sum is divisible by a given integer $K$.
  • Answer aloud and timed: Find pairs in an array whose sum is a multiple of $6$.

Technical Round 2

Candidates engage in system and database design, building domain schemas and discussing high-level architecture.

What to demonstrate

  • Candidates engage in system and database design, building domain schemas and discussing high-level architecture
  • Depth in Data Structures

How to prepare

  • Answer aloud and timed: Rotate an integer array to the right by $k$ places with optimal space complexity.
  • Answer aloud and timed: Remove all adjacent duplicates in a string repeatedly until no duplicates remain.

Fitment/HR Discussion

Final discussion to assess cultural fit and overall alignment with the company's values and expectations.

What to demonstrate

  • Final discussion to assess cultural fit and overall alignment with the company's values and expectations
  • Depth in Data Structures

How to prepare

  • Answer aloud and timed: Determine the minimum number of platforms required for a railway station given arrival and departure schedules.
  • Answer aloud and timed: Write an SQL query to retrieve the 75th, 76th, and 77th lowest salaries from an employee table.

Where candidates lose points

Think Out Loud During Coding

Never sit in silence while working through a coding problem. Talk through your initial brute-force idea, discuss time/space complexities, and explain optimizations before writing code.

Interviewers at HashedIn by Deloitte actively provide hints when you get stuck

Demonstrating receptivity to hints and pivoting your logic quickly is evaluated positively.

Master Database Schema Modeling

Practice designing complete schemas for real-world applications (e.g., Uber, Instagram, Library Systems). Focus on primary keys, foreign key constraints, bridge tables for many-to-many relationships, and normal forms.

Be Prepared to Code on Paper

Practice writing clean, syntax-accurate code on paper without rely on IDE auto-completion. Pay close attention to variable naming, boundary conditions, and line spacing.

Questions & practice

Given a string, find the length of the minimum window substring containing all required characters.

Medium · Data Structures and Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Decode an encoded string with nested repetition counts, such as expanding 3[a2[bc]] into abcbcabcbcabcbc.

Medium · Data Structures and Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Given an array of integers, find the continuous subarray whose sum is divisible by a given integer $K$.

Medium · Data Structures and Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Find pairs in an array whose sum is a multiple of $6$.

Medium · Data Structures and Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Rotate an integer array to the right by $k$ places with optimal space complexity.

Medium · Data Structures and Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Remove all adjacent duplicates in a string repeatedly until no duplicates remain.

Medium · Data Structures and Algorithms

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Determine the minimum number of platforms required for a railway station given arrival and departure schedules

Medium · Data Structures and Algorithms

Determine the minimum number of platforms required for a railway station given arrival and departure schedules.

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Compare @Controller and @RestController in Spring Boot and explain how the request lifecycle is managed in

Medium · Language and Core CS Fundamentals

Compare @Controller and @RestController in Spring Boot and explain how the request lifecycle is managed in the MVC framework.

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Describe the internal memory model of Java, focusing on garbage collection, heap management, and thread stack

Medium · Language and Core CS Fundamentals

Describe the internal memory model of Java, focusing on garbage collection, heap management, and thread stack allocation.

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

What is the difference between processes and browser tabs in modern operating systems, and how do operating sy

Medium · Language and Core CS Fundamentals

What is the difference between processes and browser tabs in modern operating systems, and how do operating systems isolate memory?

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Explain the concept of immutability and hoisting in JavaScript, along with practical usage of array methods li

Medium · Language and Core CS Fundamentals

Explain the concept of immutability and hoisting in JavaScript, along with practical usage of array methods like .map and .reduce.

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Explain object-oriented programming (OOP) principles and give real-world examples of how polymorphism is achie

Medium · Language and Core CS Fundamentals

Explain object-oriented programming (OOP) principles and give real-world examples of how polymorphism is achieved in application code.

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Write an SQL query to retrieve the 75th, 76th, and 77th lowest salaries from an employee table.

Medium · Database and SQL Design

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Design a fully normalized relational database schema for a Movie Booking System including tables, foreign keys

Medium · Database and SQL Design

Design a fully normalized relational database schema for a Movie Booking System including tables, foreign keys, and primary constraints.

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Formulate database schemas and write SQL join queries to fetch all user appointments for a specific service in

Medium · Database and SQL Design

Formulate database schemas and write SQL join queries to fetch all user appointments for a specific service in an online booking system.

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Explain database normalization levels (1NF through 3NF/BCNF) and demonstrate how to resolve transitive depende

Medium · Database and SQL Design

Explain database normalization levels (1NF through 3NF/BCNF) and demonstrate how to resolve transitive dependencies in a schema.

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Why do you want to join HashedIn by Deloitte, and how do your career goals align with our project delivery mod

Medium · Behavioral and Fitment

Why do you want to join HashedIn by Deloitte, and how do your career goals align with our project delivery model?

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

Explain the trade-offs between indexing types and demonstrate how to optimize a high-read database table.

Medium · Database and SQL Design

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Design a high-level system architecture for an app like Uber, explaining ride-matching logic and database mode

Medium · System Design and Architecture

Design a high-level system architecture for an app like Uber, explaining ride-matching logic and database modeling.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Construct the high-level architecture and schema design for a social media platform, including storage strateg

Medium · System Design and Architecture

Construct the high-level architecture and schema design for a social media platform, including storage strategies for user-generated media.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Design an end-to-end e-commerce platform detailing product catalog storage, cart management, and inventory man

Medium · System Design and Architecture

Design an end-to-end e-commerce platform detailing product catalog storage, cart management, and inventory management APIs.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Outline the architecture for a real-time food delivery app like Swiggy, focusing on order status tracking and

Medium · System Design and Architecture

Outline the architecture for a real-time food delivery app like Swiggy, focusing on order status tracking and schema normalization.

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Design a system architecture for a flight and hotel booking platform similar to MakeMyTrip.

Medium · System Design and Architecture

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Every query on one table stalls for forty seconds mid-deploy

Medium · lock contention · ddl · migrations

During a release on PostgreSQL, every query touching resource times out for about 40 seconds and then recovers with no intervention. The release ran one migration, ALTER TABLE resource ADD COLUMN archived_reason TEXT, and the migration log shows it completing in 6 ms. Unrelated tables showed no change in error rate. Explain how a 6 ms statement caused a 40-second stall, give the ordered checks you would run on a live system to confirm it, and give the migration procedure that prevents a repeat.

Approach

  1. Separate the statement's duration from the lock's duration. ADD COLUMN with no default is a catalogue-only change and genuinely runs in milliseconds, but it requires ACCESS EXCLUSIVE, and it cannot acquire that until every transaction already touching the table has finished.
  2. Account for the queueing, which is the part that surprises people. A lock request that is waiting blocks later requests for conflicting modes behind it rather than letting them overtake, so one long-open transaction holds the DDL and the DDL holds all the traffic. The stall length is set by the longest open transaction, not by the size of the change.
  3. Confirm on a live system in this order: pg_stat_activity for that table ordered by xact_start, looking for the oldest transaction and specifically for state = idle in transaction; then pg_locks where granted = false to find the waiter; then join them on pid to name blocker and blocked. pg_blocking_pids() does that join for you and is the fastest single call.
  4. Prevent rather than merely time it better. Set lock_timeout to a second or two on the migration session so the DDL abandons the queue after a bounded wait and is retried, instead of holding it for as long as the oldest transaction lives. Be exact about what that buys: queries arriving during the wait still queue behind the pending ACCESS EXCLUSIVE request, so each attempt costs them up to one lock_timeout of added latency. The outage goes from 40 seconds to about one second per attempt, not to zero. Also run migrations away from deploy-time peaks, and put a statement timeout and an idle-in-transaction timeout on the analytics role that opens the long transactions.

Follow-up

  • The same release also wants NOT NULL on that column. What is the sequence that gets there without a long lock?
  • Your lock_timeout retry fails ten times in a row because the analytics transaction is always open. What do you change?

Suggested practice checklist

Built from the rounds and topics HashedIn by Deloitte candidates report.

Day 1 — Map the HashedIn by Deloitte loop

  • Write out the reported sequence: Online Assessment, Technical Round 1, Technical Round 2, Fitment/HR Discussion.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Data Structures

  • Spend the session on Data Structures, which HashedIn by Deloitte candidates report being tested on.
  • Write one worked example in Data Structures and time yourself on it.

Deliverable: One timed worked example in Data Structures.

Day 3 — Work Algorithms

  • Spend the session on Algorithms, which HashedIn by Deloitte candidates report being tested on.
  • Write one worked example in Algorithms and time yourself on it.

Deliverable: One timed worked example in Algorithms.

Day 4 — Work Problem Solving (Approach & Thought Process)

  • Spend the session on Problem Solving (Approach & Thought Process), which HashedIn by Deloitte candidates report being tested on.
  • Write one worked example in Problem Solving (Approach & Thought Process) and time yourself on it.

Deliverable: One timed worked example in Problem Solving (Approach & Thought Process).

Day 5 — Answer out loud: Data Structures and Algorithms

  • Answer aloud, timed: Given a string, find the length of the minimum window substring containing all required characters.
  • Answer aloud, timed: Decode an encoded string with nested repetition counts, such as expanding 3[a2[bc]] into abcbcabcbcabcbc.

Deliverable: Spoken answers to 2 reported Data Structures and Algorithms question(s), under time.

Day 6 — Answer out loud: Database and SQL Design

  • Answer aloud, timed: Write an SQL query to retrieve the 75th, 76th, and 77th lowest salaries from an employee table.
  • Answer aloud, timed: Design a fully normalized relational database schema for a Movie Booking System including tables, foreign keys, and primary constraints.

Deliverable: Spoken answers to 2 reported Database and SQL Design question(s), under time.

Day 7 — Answer out loud: System Design and Architecture

  • Answer aloud, timed: Design a high-level system architecture for an app like Uber, explaining ride-matching logic and database modeling.
  • Answer aloud, timed: Construct the high-level architecture and schema design for a social media platform, including storage strategies for user-generated media.

Deliverable: Spoken answers to 2 reported System Design and Architecture question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Describe a challenging situation during a project or internship, how you handled technical ambiguity, and what

Medium · Behavioral and Fitment

Describe a challenging situation during a project or internship, how you handled technical ambiguity, and what you learned.

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

How do you manage tight project deadlines when requirements change midway through a sprint?

Medium · Behavioral and Fitment

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Explain how you collaborate with team members, handle technical disagreements, and ensure project success in a

Medium · Behavioral and Fitment

Explain how you collaborate with team members, handle technical disagreements, and ensure project success in an Agile setup.

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?