Walmart Internship to PPO Conversion Interview Experience | SDE-2 Role

I did my Summer Internship at Walmart in the AdTech department under the Data Science team. I got into this internship through the Walmart Sparkplug program, where I was fortunate to be among the Top 100 students selected. You can read my internship interview experience here Internship Process

After the internship, I appeared for the PPO (Pre-Placement Offer) Conversion Process. The process consisted of two technical rounds, followed by managerial feedback.

Round 1 – Technical (1 hour)

The interview started with introductions and then a DSA question was given to solve:

You are given a string consisting of lowercase letters, whitespaces and operators + and -. You have to evaluate the final expression and return the simplified result.

Example:

Input: a+b+a+b-a+c

Output: a+2b+c

My Approach:

• I used a 26-sized vector to store counts of each character.
• If + was before a character → increment count.
• If - was before a character → decrement count.
• Finally, I iterated over the map and constructed the result expression with non-zero counts.

Then, I compiled the code and worked well for the test cases and it also handeled the edge cases.

I discussed time & space complexity, after which the interviewer gave a follow-up:

Now extend this solution to handle brackets () along with characters and +, -.

My Follow-up Approach:

• I suggested first expanding the brackets and creating a modifed expression without brackets and then reusing my earlier function.
• For handling brackets:
  • Used a stack to manage nested expressions where stack consited of strings inside it.
  • If a negative sign appeared before a bracket, I had to negate the entire substring inside it.
  • Wrote a helper function to negate subexpressions (handling reversals and sign changes).
  • Then pushed back the entire negated expression inside the stack again
• Then iterated the stack and constructed the modifed expression and handeled the reversals while construction
• Then reused the same function defined in previous approach over this.

After debugging for 10 minutes, I got the correct output.

The interviewer said this was a hard problem and seemed happy with the solution. The round ended with some light discussions about the Walmart teams.

Later after the interview, I realized it was quite close to a LeetCode Hard problem (with integers), but here we had alphabets instead of numbers, making it more complex while performing stack operations.

Round 2 – Technical (1 hour)

Started with introductions and a short discussion of my Walmart summer internship project. Interviewer explained the flow of interview: short CS fundamental questions, then DSA, and finally database.

CS Fundamentals & Programming:

1. OOPs 4 pillars (Explanation of each)
2. Method Overloading vs Overriding
3. Deadlocks in OS
4. Memory management in C++ (delete keyword)
5. Pointers & dereferencing
6. Linked List: finding middle element using slow/fast pointer

DSA Questions:

1) Remove duplicates from a sorted array (continuous duplicates).

• First: Map-based solution (extra space).
• Then optimized: Two-pointer approach (in-place, O(1) space).
• Follow-ups:
  • Unsorted array, duplicates continuous → Same 2-pointer works.
  • Unsorted, duplicates non-continuous, no extra space →
    • I first thought of binary search.
    • Interviewer suggested sorting + reuse same function.
    • Then I gave a inary search based approach to skip insertion if key present and otherwise lower bound based sorted insertion → interviewer was impressed.

2) In a binary array, count number of subarrays with sum = target.

• First: Brute force O(n^2).
• Then: Optimized Sliding Window with 2 while loops one after other inside for loop
  • 1st while loop for expanding when sum=target but we can include next indexes if they are zero
  • 2nd while loop for shrinking the window.
• Interviewer hinted → I modified approach to:
  • countSubarrays(sum == target) = count(sum <= target) - count(sum <= target-1)
  • This worked well.
• Ran both approaches on testcases and it worked.

SQL:

Find Nth highest salary.

Answer: Use ORDER BY DESC LIMIT OFFSET with DISTINCT for duplicates.

The interview ended with me asking about the interviewer’s experience at Walmart. Before wrapping up, she asked if I would change anything about my performance in the interview so far. I mentioned the sliding window question, but she assured me that my first approach was also correct. I explained the trade-off between the two methods. She seemed happy with my reasoning and overall performance.

Wrap-up

Both rounds were purely technical.

I got very good feedback from interviewers.

Finally, I received a PPO for SDE-2 at Walmart

Key Takeaways:

Be thorough with DSA and consider all edge cases while coming up with a solution.

Revise CS fundamentals (OOPs, OS, DBMS).

Be confident in explaining your projects.

Don’t worry if your first approach is brute force — optimize step by step.

Best of luck to all future aspirants!