Watch the algorithm run, then write it.

Every lesson follows the same beats, so you always know where you are. The order matters: the idea comes first, and the syntax comes last.

1. 1

   1. Picture

   Start with one still drawing of the data, with a few handwritten notes. Before anything moves, you see the shape of the thing.

2. 2

   2. Watch

   Step through a run, one move at a time. Play it, pause it, scrub back. Nothing is hidden behind a fast animation.

3. 3

   3. Predict

   Before a step plays, you guess what happens next. Being wrong here is cheap, and it is where the idea sticks.

4. 4

   4. Try

   Type in your own input and watch the same algorithm handle it. If you can break it, you are starting to understand it.

5. 5

   5. Code

   Only now the code, in Python, Java or C++, lit up line by line in sync with what you just watched.

In every lesson the same colours mean the same roles, so once you learn them in one lesson you can read all of them. Each colour also comes with a mark or a line style, so you never have to tell them apart by colour alone.

• ▲

  Teal, with a ▲ tag below

  The first pointer: the left, slow, low or previous one.

• ▼

  Indigo, with a ▼ tag above

  The second pointer: the right, fast, high or current one.

• 7

  Coral, a solid ring

  The element being processed right now.

• 3

  Amber, a dashed outline

  Two things being compared.

• ✓

  Green, with a ✓

  The answer, or a step that worked.

• ✕

  Red, with a ✕

  A rule was broken, or an answer was wrong.

Not a judge. DSA Karle does not run or grade your code. Practice problems open on LeetCode, where you write and submit them.

No accounts. There is no sign-up and no login. The things you mark as solved and the lessons you finish stay in your browser, on this device, and nowhere else.