Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

linear time

Work that grows in proportion to the number of elements.

ArrayList.contains, indexOf, add(0, x), one full loop over a collection.