I built a free LeetCode visualizer. Here's what I learned making 207 problems animate line by line.

Rajan shukla — Sat, 11 Apr 2026 15:25:22 +0000

I spent months grinding LeetCode. I could read solutions. I could even explain them out loud. But the moment I closed the tab, it all evaporated.
The problem wasn't intelligence. It was that I was trying to understand movement through static text.
So I built codedive.in a free tool that lets you step through LeetCode problems line by line, watching everything animate in real time.
Here's what I learned building it.

The problem with how we learn algorithms

When you read a Two Sum solution, you see this:

def twoSum(nums, target):
    seen = {}
    for i, num in enumerate(nums):
        complement = target - num
        if complement in seen:
            return [seen[complement], i]
        seen[num] = i

You can follow it. But do you see it?
What you actually need to see is:

The hash map building up in real time
The complement being checked against what's already stored
The exact moment the answer is found

That's the difference between reading about swimming and being in the water.

*What codedive actually does
*

Every problem has three parts running in sync:

The code panel — each line highlights as it executes. You can step forward, backward, or scrub through at any speed.
The visualization panel — the actual data structure animates. Arrays shift. Tree nodes light up. Graph edges draw themselves.
The variable inspector — every variable in memory is visible at every step. No more guessing what left, right, mid are at step 8.

*The problems that surprised me most
*

Trapping Rain Water was the most satisfying to build. The leftMax/rightMax two-pointer approach is notoriously hard to explain in text. But when you watch the pointers move and the water level update in real time — it clicks in seconds.

What's next

Launching on Product Hunt on April 25th — follow here
Adding 100 more problems over the next 60 days
Building progress tracking and user accounts
A Pro plan for people who want the full library

If you're learning DSA or prepping for interviews give it a try. It's completely free, no login needed.
codedive.in
And if any of this was useful, I'd love your support on Product Hunt on April 25th. For a solo indie developer it means everything. 🙏

DEV Community: Rajan shukla

I built a free LeetCode visualizer. Here's what I learned making 207 problems animate line by line.