Explanations built around an animation you can step through.
An ordered route through the algorithms, with practice by pattern.
Design practice, capacity sizing, and a regex safety check.
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All 178 →Can a graph's nodes be split into two groups so every edge crosses between them? How a BFS that alternates two colours answers it in linear time, why the answer is 'no' exactly when there's an odd cycle, and the problems that are secretly this one — from scheduling to splitting people into teams.
When a DP state has to remember which items have been used, a bitmask can encode the set in one integer. How that turns the travelling salesman problem from n! routes into 2ⁿ·n states, the bit tricks you need, and how to recognise problems where n ≤ 20 is a hint.
Opening a database connection costs round trips, TLS and authentication, and every open connection costs the database memory. How a pool reuses a few connections across many requests, how to size it, what happens when it's exhausted, and why serverless and many replicas need an external pooler like PgBouncer.
Cross-site request forgery makes your browser send an authenticated request you never intended — because cookies go along automatically. How the attack works, why it doesn't need to read the response, and the defences that stop it: SameSite cookies, CSRF tokens, Origin checks, and safe GET requests.