Playlists & tracks

Learn one pattern at a time.

Ordered progressions through the problem catalogue — one pattern, a few problems, an article or two along the way. Follow a track when you want context and progression, not just a random problem list.

starter45 min · 2 steps

Hash-map lookups, from Two Sum to O(n)

The single technique that turns most brute-force loops into linear-time solutions.
two-sum· article ·why-firecracker-for-code-execution
starter30 min · 2 steps

Two-pointer walks, in and out

The pair-of-indices trick that solves half of the string and array interview questions.
reverse-stringvalid-parentheses