My First Technical Interview (AlgoUniversity)

Today I gave my first ever technical interview for an SDE intern role at AlgoUniversity.

There were 2 DSA questions and 2 CS fundamentals (OS + OOP).

This is a straightforward breakdown of what was asked, what I thought, what was right, and what I missed.

DSA Question 1 — Search in Infinite Sorted Array

Problem

Sorted array (monotonically increasing, unique).
Length unknown (conceptually infinite).
Given a target → return index or -1.

Example:

arr = [2, 5, 9, 14, 21, 37, 58, 73, 91, ...]
target = 37 → 5

What I thought

Binary search is ideal since sorted.
But right boundary unknown.

So I tried expanding range exponentially:

while (arr[last] < target)
    last *= 2;

I actually wrote this part correctly.

But I embedded it inside a binary search loop instead of treating it as a separate phase:

while (first < last) {
    while (arr[last] < target)
        last *= 2;

    mid = (first + last) / 2;
    // binary search logic
}

What was right

Realized boundary must be discovered
Used exponential growth (correct idea)

What was wrong

Mixed range expansion with binary search
Didn’t separate phases

Correct structure

Expand range exponentially
Binary search inside range

Learning

When array size unknown → exponential search first, binary search later.
Structure matters as much as idea.

DSA Question 2 — Minimum Cost Grid Path

Problem

n×n grid with costs.
Start: (0,0)
End: (n−1,n−1)
Move in 4 directions.
Minimize total cost.

Example:

1 3 1
2 1 4
3 2 1

What I thought

Grid → graph
Cell → node
Neighbors → edges
Cost → weight

So I chose Dijkstra.

Started with direction arrays:

dirX = {1,0,0,-1}
dirY = {0,1,-1,0}

Then I drifted toward BFS + “pick smallest each stage”.

What was right

Correct modeling
Correct algorithm choice (Dijkstra)

What was wrong

Forgot priority queue implementation
Couldn’t recall Dijkstra mechanics

Learning

Knowing algorithm name ≠ implementing it.
Need recall fluency for core algorithms (Dijkstra, BFS, DFS).

OS Question — 2GB RAM Running 5GB Game

Question

How can a 2GB RAM laptop run a 5GB game?

My answer

Swap memory on disk acting like extra RAM.

Evaluation

Correct concept.

Full idea: virtual memory → inactive pages moved to disk.

Learning

OS fundamentals are mostly clear.

OOP Question — Virtual Destructors

Question

What is a virtual destructor and why important?

My answer

I misunderstood and talked about auto type deduction.
So this was wrong.

Correct concept

If deleting via base pointer:

Base* b = new Derived();
delete b;

Without virtual destructor → only base destroyed.
Derived cleanup skipped → leak.

Learning

Need stronger OOP fundamentals recall.

Interview Feedback

Interviewer said:

Improve DSA
Talk more and discuss approach
He would give hints if I interacted more

Overall Learning

I was often structurally close in DSA
Main gaps: recall + articulation
Need practice implementing core graph algorithms
Need to think aloud in interviews

First technical interview → clear direction now.