◈DSA Studio
Sign inCreate account
A QUIET PLACE FOR DATA STRUCTURES & ALGORITHMS

Read the problem.
Make it make sense.

Work through the patterns. Think on paper. Try it in Python.
Keep the thinking that gets you there.

Explore the problems Make yourself a desk
Browse freely. Sign in when you’re ready to write.
Two Sum Arrays & Hashing
FIRST THOUGHTS

What am I really
looking for?

a pair that adds up to 9
2+7=9
Remember what I’ve seen.
Look for what’s missing.
O(n) time · one pass
PYTHON
# A thought becomes code.
seen = {}

for i, n in enumerate(nums):
    needed = target - n

    if needed in seen:
        return [seen[needed], i]

    seen[n] = i
✓ Thinking, kept.
YOUR NOTES. YOUR CODE. SIDE BY SIDE.
A LITTLE DIRECTION

Start small. Go deeper.

Three paths through the same patterns.
Choose the depth that feels right.

◈75 problems ↗

Core

The essential patterns. A focused foundation.

Explore the path
⌘150 problems ↗

Mastery

Build fluency. Connect the patterns.

Explore the path
✧250 problems ↗

Beyond

A wider range. A deeper understanding.

Explore the path
ROOM TO UNDERSTAND

More than the
right answer.

Leave a trail of thought.

A roomy notebook for words, sketches, and the moment it clicks. Your notes stay with each problem.

See your idea run.

Write Python beside your notes. Inspect the sample cases, compare results, and keep versions of your approach.

Come back with fresh eyes.

Save your progress and revisit what needs another look. Your desk is here when you return.

One problem. A fresh page.

Find your starting point