AT&T Software Developer Interview Questions and Answers

Round duration - 15 minutes
Round difficulty - Easy

This was a group discussion round where we were divided into groups of 10 and we had 15 minutes for GD.

Round duration - 60 minutes
Round difficulty - Medium

This is all about how good you are with the fundamentals. Out of 10 I would give it a 6.5 on difficulty.

Q1. 
Reverse the String Problem Statement
You are given a string STR which contains alphabets, numbers, and special characters. Your task is to reverse the string.
Example:
Input:
STR = "abcde"
Output:
"e...read more
Ans. 
Reverse a given string containing alphabets, numbers, and special characters.
• Iterate through the string from the end to the beginning and append each character to a new string.

• Use built-in functions like reverse() or StringBuilder in languages like Python or Java for efficient reversal.

• Handle special characters and numbers while reversing the string.

• Ensure to consider the constraints on the length of the string and the...read more
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Q2. What is a deadlock?
Ans. 
A deadlock is a situation in which two or more processes are unable to proceed because each is waiting for the other to release a resource.
• Occurs in multitasking environments where processes compete for limited resources

• Can be resolved using techniques like deadlock prevention, deadlock avoidance, and deadlock detection

• Example: Process A holds Resource X and waits for Resource Y, while Process B holds Resource Y and wa...read more
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Q3. What is a thread?
Ans. 
A thread is a lightweight sub-process that allows concurrent execution within a single process.
• Threads share the same memory space within a process.

• Threads are used to achieve parallelism and improve performance.

• Examples of threads include the main thread in a program and worker threads in a multi-threaded application.
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Q4. What is the difference between Multiprocessing and Multiprogramming?
Ans. 
Multiprocessing involves multiple processors executing multiple tasks simultaneously, while multiprogramming involves multiple programs sharing a single processor by switching between them.
• Multiprocessing utilizes multiple processors to execute multiple tasks concurrently.

• Multiprogramming involves multiple programs sharing a single processor by switching between them.

• Multiprocessing is more efficient in terms of perfor...read more
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Q5. Can you explain the process life cycle in an operating system?
Ans. 
Process life cycle in an operating system involves creation, execution, termination, and resource management.
• Creation: When a process is created, it is assigned a unique process ID and allocated necessary resources.

• Execution: The process is then scheduled by the operating system to run on the CPU.

• Termination: Once the process completes its task or is terminated by the user, it is removed from memory.

• Resource Management...read more
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Q6. What are the differences between Windows XP and Windows 7?
Ans. 
Windows XP and Windows 7 are both operating systems developed by Microsoft, but they have several key differences.
• User interface: Windows 7 has a more modern and user-friendly interface compared to Windows XP.

• Performance: Windows 7 is generally faster and more stable than Windows XP.

• Security: Windows 7 has more advanced security features and updates compared to Windows XP.

• Hardware support: Windows 7 supports newer hard...read more
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Round duration - 60 minutes
Round difficulty - Easy

Technical round with questions on DBMS and Networking mainly.

Q1. What is the difference between RDBMS and DBMS?
Ans. 
RDBMS is a type of DBMS that stores data in a structured format with relationships between tables.
• RDBMS enforces referential integrity and allows for normalization of data.

• DBMS is a general term for any system that manages databases, while RDBMS specifically refers to relational databases.

• Examples of RDBMS include MySQL, Oracle, and SQL Server.

• Examples of DBMS include MongoDB and Redis.
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Q2. What is an Object-Oriented Database Management System (OODBMS)?
Ans. 
An Object-Oriented Database Management System (OODBMS) is a type of database management system that supports the creation and management of objects in a database.
• OODBMS stores data in the form of objects, which can contain attributes and methods.

• It allows for complex data structures and relationships to be represented more easily.

• Examples of OODBMS include db4o, ObjectDB, and ObjectStore.
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Q3. How do you find the number of unique values in a SQL database?
Ans. 
Use the COUNT DISTINCT function in SQL to find the number of unique values in a database.
• Use the COUNT DISTINCT function along with the column name to count the number of unique values in that column.

• For example, SELECT COUNT(DISTINCT column_name) FROM table_name;

• You can also use GROUP BY to find the number of unique values for multiple columns.
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Q4. What is the difference between a hub and a switch in networking?
Ans. 
A hub operates at the physical layer and broadcasts data to all devices on the network, while a switch operates at the data link layer and forwards data only to the intended recipient.
• Hub operates at the physical layer, while switch operates at the data link layer

• Hub broadcasts data to all devices on the network, while switch forwards data only to the intended recipient

• Switch is more efficient and secure compared to a ...read more
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Q5. Can you explain the different OSI layers?
Ans. 
The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven different layers.
• Physical Layer: Deals with the physical connection between devices. Example: Ethernet cables.

• Data Link Layer: Responsible for node-to-node communication. Example: MAC addresses.

• Network Layer: Manages routing of data packets. Example: IP addresses.

• T...read more
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Q6. What are the different protocols supported at each OSI layer?
Ans. 
Different protocols supported at each OSI layer
• Layer 1 (Physical): Ethernet, Wi-Fi, Bluetooth

• Layer 2 (Data Link): MAC, PPP, HDLC

• Layer 3 (Network): IP, ICMP, ARP

• Layer 4 (Transport): TCP, UDP, SCTP

• Layer 5 (Session): NetBIOS, PPTP

• Layer 6 (Presentation): SSL, TLS

• Layer 7 (Application): HTTP, FTP, SMTP
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Round duration - 15 minutes
Round difficulty - Easy

IF you make it to the HR round you are selected. All 28 that attended got selected . It was more like stuff for formality. The usual questions.

Mcq based on language

Q1. Do you know STL. Find loop in linked list.
Ans. 
STL knowledge and finding loop in linked list
• STL (Standard Template Library) is a C++ library that provides containers, algorithms, and iterators.

• To find a loop in a linked list, we can use Floyd's cycle-finding algorithm.

• In this algorithm, we use two pointers, one moving at a slower pace and the other at a faster pace.

• If there is a loop in the linked list, the faster pointer will eventually catch up to the slower poin...read more
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Round duration - 90 minutes (60 minutes for coding and 30 minutes for MCQs)
Round difficulty - Medium

The test was conducted in the evening from 7:00 pm to 8:30 pm. Because of the covid situation, the test was online and was given by all the students from their home. 
Login window of 15 minutes was given and all students were supposed to login within initial 15 minutes (between 7:00 and 7:15 pm). The test was conducted on AMCAT and webcam was on during the whole test duration.
There were two sections in the test: 1.) Coding round with 2 coding questions - 60 minutes (2.) MCQ round with 30 MCQs - 30 minutes
120 students appeared for this round and 20 were shortlisted for further process.

Q1. 
Character Frequency Problem Statement
You are given a string 'S' of length 'N'. Your task is to find the frequency of each character from 'a' to 'z' in the string.
Example:
Input:
S : abcdg
Output:
1...read more
Ans. 
Given a string, find the frequency of each character from 'a' to 'z' in the string.
• Create an array of size 26 to store the frequency of each character from 'a' to 'z'.

• Iterate through the string and increment the count of the corresponding character in the array.

• Print the array of frequencies as the output for each test case.
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Q2. 
Longest Common Prefix After Rotation
You are given two strings 'A' and 'B'. While string 'A' is constant, you may apply any number of left shift operations to string 'B'.
Explanation:
Your task is to calcu...read more
Ans. 
Calculate the minimum number of left shift operations needed to achieve the longest common prefix between two strings.
• Apply left shift operations to string B to find the longest common prefix with string A

• Count the number of left shifts needed to achieve the longest common prefix

• Return the minimum number of left shift operations for each test case
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Round duration - 50-60 minutes
Round difficulty - Medium

This round started at 11 am and went till 3 pm. 
Out of 120 students that appeared in online coding test, 20 were shortlisted for the first round of interviews.
In this round, everyone was asked some moderate level coding questions. We were supposed to write the code in our IDE, present the screen and show the interviewer the output of our code.
The interview started with the introduction being followed by 2 coding problems.

Q1. 
Longest Subarray with Zero Sum
Ninja enjoys working with numbers, and as a birthday challenge, his friend provides him with an array consisting of both positive and negative integers. Ninja is curious to ...read more
Ans. 
Find the length of the longest subarray with zero sum in an array of integers.
• Iterate through the array and keep track of the running sum using a hashmap.

• If the running sum is seen before, the subarray between the current index and the previous index with the same sum is a subarray with zero sum.

• Update the length of the longest subarray with zero sum as you iterate through the array.

• Example: For arr1 = [1, -1, 3, 2, -2...read more
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Round duration - 20 minutes
Round difficulty - Medium

7 students were shortlisted for the HR round. This round started at 7:30 pm and went till 8:30 pm.
Like all the other rounds, this round too was virtual (on google meet). In the beginning, the interviewer introduced himself and then asked questions based on my resume.
All the 7 candidates were selected in the HR round.

Q1. All basics which language you know?
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Q2. Ready to learn and work ?
Ans. 
Yes, I am ready to learn and work.
• I am highly motivated and eager to expand my knowledge and skills.

• I am open to learning new technologies and programming languages.

• I am willing to take on challenging projects and work collaboratively with a team.

• I have a track record of quickly adapting to new environments and delivering high-quality software solutions.
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Q3. Able to handle work pressure?
Ans. 
Yes, I am able to handle work pressure.
• I prioritize tasks and manage my time effectively

• I communicate with my team and ask for help when needed

• I take breaks and practice stress-relieving techniques

• I stay organized and focused on the end goal
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Q1. Which tech stack you worked ?
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Q2. Crucial work which you done in your career?
Ans. 
Developed a critical software module for a large e-commerce platform.
• Designed and implemented a secure payment gateway integration.

• Optimized database queries to improve performance by 50%.

• Resolved a major bug that was causing system crashes.

• Implemented a real-time chat feature using WebSockets.

• Developed an automated testing framework to ensure code quality.
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Q3. How to manage your work ?
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DSA and javasciript questions

Q1. Questions on closure, javascript event loop, promises, async await, callbacks,
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Q1. Why looking for job change?
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Just basic quants and maths was in the test

Q1. Based on projects
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Q1. Behavioral questions were asked and what do you know about the company
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