A free coding interview game

Can you solve Two Sum without AI?

Write twoSum the way you would on LeetCode. Booly the cat runs it one line at a time, and every time your code reads nums[i], he walks over to that treat. Then make it fast enough for a hungry cat, and take on four more classic patterns: two pointers, binary search, one pass and a sliding window.

Free, no sign-up, no AI. Progress is saved in this browser.

Hi. I'm Booly. Two of my treats add up to my target. Find them. Every look costs me a walk, so make it quick.
<BOOLY>// CODING CAT0110101011010101

What you'll practice

  1. Level 1-1Two SumLists, a dict, and why one pass beats two loops.
  2. Level 1-2Two Sum IIA sorted row: two pointers, and no notebook.
  3. Level 1-3Binary SearchA sorted row of 16: throw away half with every look.
  4. Level 1-4Best Time to Buy and SellPrices: remember the cheapest day so far.
  5. Level 1-5Max Sum of KA window of k treats: slide it, drop one, add one.

How it works

  • Write twoSum in the editor, the way you would on LeetCode. The starting code has class Solution ready.
  • Press Run. Each time your code reads nums[i], Booly walks to that treat, and the look counter goes up.
  • Three stars: find the pair in every room, walk the row in linear time, and do it in one pass.

Questions

Is it real Python?
Yes: classes, lists, dicts, sets, loops, if and functions, as in LeetCode's Python. It runs right in your browser, with no AI to help.
Can I paste my LeetCode solution?
It runs, and pasted code gets one star. Type it yourself for all three: that's the "without AI" part.
Who is it for?
Anyone preparing for coding interviews, and anyone who finds problems like Two Sum hard. That's normal, and it's exactly what practice fixes.
What comes after?
AlgoCademy's Two Sum lesson walks through it step by step. The first step is free.