Blog

LeetCode 56 merges [1,4] and [4,5]; LeetCode 435 says they do not overlap at all. Closed versus half-open ends is the one real decision in interval problems, and most interval bugs come from never making it.

Client-side validation is UX. Server-side validation is security. And a schema is not an auth guard — here's the fix that still ships an account takeover, and how to catch it in review.

A monotonic stack maintains elements in order and pops when that order breaks — finding the next greater element for every popped value in O(n) total.

Reading a 2 GB file all at once doesn't run out of memory — it hits V8's 512 MB string limit first. Streams process it in flat memory instead. Here's the pipeline pattern, custom Transform streams, and backpressure, with the numbers measured on Node 22.

The EventEmitter pattern lets components in the same process react to the same event without being directly coupled — no message broker needed.

One file to guard every route — plus the Next.js 16 rename that moves it off the Edge runtime, the request-vs-response header trap that leaks user IDs to the browser, and the CVE that explains why this can never be your only auth layer.

Parallel routes let a single layout render multiple independent pages at once. Combine them with intercepting routes and you get URL-aware modals with zero hacks.

Node.js runs on one CPU core by default. The cluster module lets you fork N workers across all cores — here's the pattern, graceful shutdown, IPC, and when PM2 makes it unnecessary.

Server Actions collapse form handling into a single server function—no API route, no manual fetch, no useState for loading. Here's the pattern that replaces 80% of your mutation boilerplate.