Barclays interview experience Real time questions & tips from candidates to crack your interview
SDE - Intern
Barclays
3 rounds | 9 Coding
problems
Selected Interview preparation journey
Journey
When I entered college, I had very little clarity about Computer Science. Apart from basic C++ from a junior college elective, I was mostly clueless. I didn’t have proper guidance on what actually matters for internships, so my early learning was quite haphazard.
In my first year, I explored things like cloud computing and neural networks out of curiosity, without having strong fundamentals. It kept me interested, but I later realized I was building without a solid base. In second year, I moved on to Operating Systems and Web Development. While I enjoyed development, I wasn’t consistent with DSA, which many peers were already focusing on.
One thing that worked in my favour was my serious preparation of CS fundamentals at a GATE level—subjects like OS, DBMS, CN, and COA. At the time, I didn’t realize how important this would become.
The turning point was understanding what interviews—especially for intern roles—actually expect. More than advanced development skills, interviewers look for:
- Strong CS fundamentals
- Logical thinking and problem-solving
- Ability to explain concepts clearly
- Decent (not necessarily expert) development knowledge
Once I understood this, my preparation became more focused. Instead of trying to cover everything, I revised core subjects, strengthened DSA basics, and focused on understanding why things work. My fundamentals helped me reason through questions, even when I didn’t know answers directly.
Cracking the interview wasn’t about knowing every tool or framework; it was about showing strong foundations, clarity of thought, and willingness to learn.
If there’s one takeaway from my journey: Fundamentals matter more than hype, and a confused start doesn’t stop you from reaching a strong finish.
Application story
During my second year, I participated in the Barclays Hack-o-Hire Hackathon and our team advanced to the final round. Throughout the event, we worked closely with mentors who observed our approach to problem-solving and execution. They appreciated our performance, clarity of thought, and overall problem-solving mindset, which led them to invite us for the interview after the hackathon.
Why selected/rejected for the role?
I believe I was selected not because I knew everything, but because I demonstrated strong fundamentals, clarity of thought, and the ability to reason through problems. My preparation in core CS subjects helped me approach questions logically and explain my thinking clearly.
Additionally, my experiences through projects and hackathons showed that I could apply concepts in practical scenarios, work through ambiguity, and learn quickly. I was honest about what I knew, confident in my strengths, and open about areas where I was still learning - something interviewers value highly.
Overall, it was the combination of solid CS foundations, problem-solving mindset, and a genuine willingness to grow that set me apart.
Preparation
Duration: 2 months
Topics: Data Structures, OOPS, DBMS, System Design, Spring Boot, C++, Operating System, Java, Puzzles, SQL
Tip 1: Know the tool as well as the design patterns and system intricacies that drive it.
Tip 2: Showcase projects that are industry oriented and consists of a niche technical concept.
Application process
Where: Campus
Eligibility: NA, (Stipend: 75k per month)
Tip 1: Don’t list a plethora of programming languages, tools, or technologies just due to peer pressure. Be honest and own what you truly know. Depth always matters more than breadth.
Tip 2: Aim to build a holistic profile as a fresher. Include meaningful experiences such as hackathons, projects, open-source contributions, internships, publications, or research work to showcase your curiosity and initiative.
Interview rounds
01
Round
Medium
Face to Face
Duration30 minutes
Interview date11 Sep 2024
Coding problem3
1. Group Anagrams
Moderate
30m average time
70% success
0/80
Asked in companies
You have been given an array/list of strings 'inputStr'. You are supposed to return the strings as groups of anagrams such that strings belonging to a particular group are anagrams of one another.
An anagram is a word or phrase formed by rearranging the letters of a different word or phrase. We can generalize this in string processing by saying that an anagram of a string is another string with the same quantity of each character in it, in any order.
Note:
The order in which the groups and members of the groups are printed does not matter.
For example:
inputStr = {"eat","tea","tan","ate","nat","bat"}
Here {“tea”, “ate”,” eat”} and {“nat”, “tan”} are grouped as anagrams. Since there is no such string in “inputStr” which can be an anagram of “bat”, thus, “bat” will be the only member in its group.
Problem approach
Step 1: Clarified the requirement + edge cases
I confirmed whether the output should be:
Grouped anagrams (vector>), or
A single vector containing strings arranged so anagrams are together.
I also checked edge cases: empty input, single string, repeated strings, different lengths.
Step 2: Started with the brute-force idea
I first thought of comparing each string with every other string.
Two strings are anagrams if their sorted versions are equal.
This leads to O(n² * k log k) time (n strings, each length k), which is too slow for larger inputs.
Step 3: Optimized using hashing (key idea: canonical form)
I realized every anagram group shares a common “signature”.
I used the sorted string as the signature/key.
Example: "eat" -> "aet", "tea" -> "aet", "tan" -> "ant".
I stored results in an unordered_map> where:
key = sorted string
value = list of original strings belonging to that group
Step 4: Built the final answer from the map
After processing all strings, I iterated over the hashmap values and pushed them into the answer vector.
Step 5: Explained complexity clearly
Sorting each string costs O(k log k), repeated for n strings → O(n * k log k) time.
Hashmap storage takes O(n * k) space overall.
Step 6 (optional improvement if asked): frequency count signature
If interviewer asked to optimize further, I mentioned using a 26-length frequency array as key for lowercase strings (e.g., #1#0#2...) to avoid sorting:
Time becomes O(n * k) (linear per string).
2. DBMS
I was given a UI design/mock flow of a pharmaceuticals website (pages like product listing, product details, cart/checkout, prescriptions, orders, etc.) and was asked to design a relational database schema for it. The expectation was to identify entities, relationships, constraints, and normalization, and justify design choices
3. Puzzle
Given two jugs with capacities X and Y litres and an unlimited water supply, determine whether it is possible to measure exactly Z litres of water using only the following operations:
- Fill a jug completely
- Empty a jug
- Pour water from one jug to another until either the source is empty or the destination is full
02
Round
Hard
Face to Face
Duration60 minutes
Interview date11 Sep 2024
Coding problem5
This was a round focused on C++ fundamentals and OS.
1. Operating System
Explain Byte padding & alignment.
2. C++
- new operator vs malloc
- inline over macros
- Preprocessor directives
- const
- constexpr
4. Computer Organization
What are Stack frames? What’s inside a stack frame? What is stack pointer vs frame pointer? (Learn)
5. DLL
Explain DLL marshalling (COM).
03
Round
Medium
Assignment
Duration1 day
Interview date7 Oct 2024
Coding problem1
Each team has to submit a pitch deck corresponding to a particular problem statement from the four below:
- Email Classification and Routing System Integrated in Outlook
- Anomaly Detection Framework - System to identify irregularities in trade data
- Mobile applications likely for multi-channel banking solutions integrating various platforms for seamless user experiences in financial services
- Predicting and forecasting threats or cyber attacks, involving analysis of cybersecurity events like threat identification from email datasets
The ones selected, will be participating in the prototype development phase at Barclays LTS campus.
We were given 24 hours to build the product, create the presentation and concerned artifacts. Mentors analysed the performance of every individual in each team and the ones performing better were given PPI opportunities.
1. System Design
Organizations and individuals face a growing challenge with the sheer volume of incoming email. Many messages arrive with different categories or labels, yet users still must manually classify these emails and then route them to the right recipients. This process is repetitive, error-prone, and steals time from more meaningful work. There is a need for a solution that can automatically classify incoming messages by their assigned category and route them in organized batches to their intended recipients, streamlining communication and improving productivity.
Problem approach
The solution automates email handling by integrating with Microsoft Exchange Server to access organizational mailboxes and using Microsoft Graph API to securely fetch email content. Each message is semantically classified using DistilBERT, enabling accurate understanding of intent and category. Lightweight backend logic, hosted via Azure Functions, then applies routing rules to distribute emails in bulk to the appropriate recipients, reducing manual effort while preserving clarity and control.
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