1. Write a JOIN query to combine Employees and Departments tables and find department-wise average salary.
Use INNER JOIN with AVG() and GROUP BY.

2. Use RANK() function to rank employees by salary within each department.
RANK() OVER(PARTITION BY department_id ORDER BY salary DESC).

3. Write a query using GROUP BY and HAVING to find departments with more than 5 employees.
GROUP BY department_id HAVING COUNT(*) > 5.

4. Delete duplicate rows using ROW_NUMBER() window function.
Use ROW_NUMBER() OVER(PARTITION BY duplicate_columns ORDER BY id) and delete where rn > 1.

5. Write a correlated subquery to find employees earning more than their department average.
SELECT * FROM employee e WHERE salary > (SELECT AVG(salary) FROM employee WHERE dept_id = e.dept_id).

6. Explain the assessment SQL query you wrote. What was the condition and how did you implement it?
Be prepared to walk through your exact assessment solution step-by-step.

7. Write a query with CASE WHEN to categorize employees by salary range.
CASE WHEN salary > 100000 THEN 'High' WHEN salary > 50000 THEN 'Medium' ELSE 'Low' END.

8. Find the second highest salary using different approaches (subquery, DENSE_RANK, LIMIT/OFFSET).
SELECT MAX(salary) FROM employee WHERE salary < (SELECT MAX(salary) FROM employee);

9. Explain different types of JOINs with examples. When would you use LEFT vs INNER?
INNER returns matching rows; LEFT returns all from left table with NULLs for non-matching right.

10. Handle NULL values in queries. Difference between IS NULL and = NULL.
IS NULL is correct; = NULL always returns false because NULL is not equal to anything.

• Master Window Functions: Practice RANK, DENSE_RANK, ROW_NUMBER, and aggregations with OVER().
• Practice Complex JOINs: Be comfortable with multi-table JOINs, self-JOINs, and subqueries.
• Optimize Query Performance: Understand execution order, indexing, and avoid N+1 queries.
• Explain Your Logic: Be ready to write SQL on a whiteboard or shared screen and explain each clause.

1. Check if a string is a palindrome (asked for 3-4 different approaches).
Two-pointer, reverse string, recursion, stack-based approaches.

2. Find non-anagram strings from an array. Implement end-to-end with optimal approach.
Use sorted string as hashmap key; collect values with count = 1.

3. Find the longest palindrome in a string.
Expand around center (O(n²)) or Manacher's algorithm (O(n)).

4. Reverse a string without using built-in functions.
Two-pointer swap from both ends.

5. Two Sum problem: find two numbers that add up to target.
Hashmap approach O(n) or brute force O(n²).

6. Discuss time and space complexity for each solution.
Be prepared to explain Big-O for every approach.

7. Perform a detailed dry run to validate your logic.
Walk through each step with sample input to demonstrate correctness.

• Know 3-4 Approaches Per Problem: ZS interviewers explicitly ask for multiple solution strategies.
• Master Complexity Analysis: Always state time and space complexity before coding.
• Practice Whiteboard Coding: Write clean, syntactically correct code without an IDE.
• Dry Run Thoroughly: Walk through your code step-by-step with sample inputs to prove correctness.

1. Predict output of code snippets involving inheritance and polymorphism.
Understand method resolution order, super() calls, and dynamic dispatch.

2. What is the difference between abstract class and interface?
Abstract class can have implementation; interface defines contract only (pre-Java 8).

3. Explain method overriding with an example. What is dynamic dispatch?
Runtime polymorphism where JVM determines which method to call based on object type.

4. What are access modifiers? Explain scope of each.
public, private, protected, default (package-private).

5. Explain encapsulation, inheritance, abstraction, and polymorphism.
Four pillars of OOP with real-world examples.

• Practice Output Prediction: Run code snippets mentally and trace inheritance chains.
• Understand Polymorphism Deeply: Know compile-time vs runtime polymorphism.
• Use Real-World Examples: Explain OOP concepts with practical analogies.
• Know Java/C++ Specifics: Access modifiers, virtual methods, and constructor chaining.

1. How many squares are on a chessboard?
Answer: 204 (1² + 2² + ... + 8²).

2. How many single-colored squares are on a chessboard?
32 black + 32 white = 64 total single-colored squares.

3. Water bucket puzzle: You have 3L and 5L jugs. Measure exactly 4 liters.
Fill 5L, pour to 3L (2L left), empty 3L, pour remaining 2L to 3L, fill 5L, pour to 3L until full (1L added), 4L remains.

4. Monty Hall problem: Should you switch doors? Explain probability.
Switch gives 2/3 chance; stay gives 1/3. Conditional probability explanation.

5. 12 balls puzzle: One is different weight. Find it in 3 weighings.
Divide into 3 groups of 4; use balance scale with binary search logic.

6. Two ropes burn in 1 hour each (non-uniform). Measure 45 minutes.
Light rope A both ends and rope B one end. When A burns out (30 min), light B other end. B finishes in 15 more minutes.

7. How many times do clock hands overlap in 24 hours?
22 times (11 times per 12-hour period).

• Practice Classic Puzzles: Focus on weighing puzzles, clock problems, probability puzzles, and water jug problems.
• Explain Reasoning Step-by-Step: Walk through your thought process clearly.
• Use Structured Approach: Break down the problem, identify constraints, and build solution incrementally.
• No Guesswork: If stuck, explain the approach rather than guessing the answer.

1. Estimate the number of bikes in Bangalore.
Use population, household size, and bike ownership percentage.

2. How many traffic signals are in Pune?
Estimate intersections per sq km × city area.

3. Estimate the number of people traveling in Delhi Metro at 9 AM.
Consider number of trains, coaches, capacity, and occupancy rate during peak.

4. How many planes depart from Trivandrum Airport daily?
Use number of gates, turnaround time, and operational hours.

5. Estimate the volume of the chair you are sitting in.
Approximate as rectangular prism (length × width × height).

6. How many phones are sold in India per year?
Use population, replacement cycle, and penetration rate.

7. Estimate the number of ATMs in your city.
Use bank branches per capita × ATMs per branch.

• Structure Your Estimate: Start by defining assumptions clearly.
• Use Population-Based Approach: Most guesstimates can be anchored to population data.
• Show Calculations: State each multiplication or division step audibly.
• Sanity Check Results: Ask if the final number seems reasonable.
• Practice the Framework: Market sizing uses the same structured thinking as ZS client work.

1. You are working on a project for 6 months and discover a technical error the day before launch. What do you do?
Assess impact, communicate with stakeholders, propose mitigation plan.

2. How would you approach a pharmaceutical project scenario using SDLC methodology?
Walk through requirements gathering, design, development, testing, deployment phases.

3. You are assigned as team leader for a new project. Walk through your step-by-step approach.
Understand scope, assemble team, set milestones, establish communication, manage risks.

4. A client is unhappy with the delivered solution. How do you handle it?
Listen actively, acknowledge concerns, assess gaps, create remediation plan.

5. You find redundant or missing data in a database table. How do you identify and fix the issues?
Profile data, identify anomalies, clean with deduplication or imputation, document changes.

• Use STAR Framework: Situation, Task, Action, Result for behavioral responses.
• Think Out Loud: Interviewers want to see your reasoning process.
• Prioritize Structured Thinking: Break problems into smaller parts and address each.
• Show Business Acumen: Connect decisions to client impact and stakeholder satisfaction.

1. Explain your most significant project in detail.
Walk through problem statement, approach, implementation, and results.

2. What CNN/ML model did you use in your project? (if applicable) In-depth technical questions.
Be ready for deep technical dives on model architecture, hyperparameters, and evaluation metrics.

3. What Python libraries did you use? Explain specific functions.
Know pandas, numpy, sklearn, matplotlib functions you claim to have used.

4. What challenges did you face and how did you overcome them?
Describe real obstacles and specific solutions implemented.

5. If you had more time, how would you improve your project?
Show growth mindset with concrete enhancement ideas.

6. Explain your internship contributions across projects.
Quantify impact with metrics and deliverables.

• Know Your Resume Inside Out: Every line on the resume is fair game for deep questioning.
• Prepare Project Deep-Dives: Have a 2-minute and 5-minute version of each project explanation.
• Quantify Impact: Use numbers, metrics, and concrete outcomes.
• Never Fake Experience: ZS interviewers are known for intense resume probing.
• Connect Projects to ZS Work: If possible, relate your project experience to ZS's consulting and analytics work.