Algorithms & Big O Notation

Look up what an algorithm actually costs, then watch it run. Lichen is a quiet, dark reference and drill app for time and space complexity that works entirely on your device. THE CATALOG Thirty classic algorithms across sorting, searching, graphs, trees, strings, dynamic programming, hashing, heaps and greedy methods. Each entry gives you best, average and worst case complexity, space cost, readable pseudocode, a plain-English explanation of how it works, and the situations where you would actually reach for it. Filter by category or by complexity class, or search by name to jump straight to Quick Sort, Dijkstra, Rabin-Karp or Floyd-Warshall. STEP THROUGH IT Sorts, binary search, linear search, BFS and DFS animate frame by frame from instrumented implementations, not canned video. Play, pause, scrub back to the step you missed, slow the speed down, and feel every comparison and swap through haptics. Watching Merge Sort divide and recombine makes n log n stop being an abstraction. SEE THE CURVES One growth chart plots O(1), O(log n), O(n), O(n log n), O(n squared), O(2^n) and O(n!) together. Toggle classes on and off and highlight a single line to see just how violently the curves separate as n grows. DRILL WHAT YOU FORGET The quiz asks you for the complexity of a given algorithm and scores you. Anything you flag as shaky resurfaces more often, and per-topic accuracy shows where your gaps really are. Your study history is written to the device and nowhere else. SAVE FOR LATER Bookmark the algorithms you keep coming back to and keep them in one list. BUILT FOR Computer science students facing an exams week, bootcamp graduates, self-taught engineers filling in the theory, and anyone brushing up before a technical loop. No account, no sign-in, no network calls, no ads. Portrait, dark, and fast enough to check something between train stops. UNLOCK Algorithms & Big O Notation requires a Pro unlock to study. Pro opens the complete app: the full catalog of thirty algorithms with best, average and worst case complexity, space cost, pseudocode and plain-English explanations, the step-through visualizer with play, pause, scrub and speed control, the growth chart across every complexity class, the quiz with per-topic accuracy and resurfacing of what you flag as shaky, and bookmarks. Plans: a weekly subscription, a yearly subscription, or a one-time lifetime purchase. Payment is charged to your Apple ID account at confirmation of purchase. The subscription renews automatically unless it is cancelled at least 24 hours before the end of the current period, and your account is charged for renewal within 24 hours prior to the end of the current period. You can manage your subscription and turn off auto-renewal in your Account Settings after purchase. Privacy policy: https://pnkl26.web.app/privacy-policy Terms of use: https://pnkl26.web.app/terms-of-service