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

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:

1. The code panel — each line highlights as it executes. You can step forward, backward, or scrub through at any speed.
2. The visualization panel — the actual data structure animates. Arrays shift. Tree nodes light up. Graph edges draw themselves.
3. 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. 🙏