Programming

Hash maps are the most useful data structure for coding interviews. If you can only master one data structure beyond arrays, make it hash maps. They give you O(1) average-time lookups, insertions, and deletions. Many interview problems that seem hard become easy once you use a hash map. In this article, you will learn how hashing works, when to use hash maps vs hash sets, and how to solve classic interview problems. We show every example in Kotlin, Python, and Go. ...

Stacks and queues are two of the most fundamental data structures in computer science. They are building blocks for many algorithms and appear frequently in coding interviews. The rules are simple — stacks follow Last In, First Out (LIFO), and queues follow First In, First Out (FIFO). In this article, you will learn how stacks and queues work, how to implement them, and how to solve classic interview problems. We show every example in Kotlin, Python, and Go. ...

Linked lists are the second most common data structure in coding interviews after arrays. They test your ability to work with pointers, handle edge cases, and think about memory. In this article, you will learn how linked lists work, how to implement them, and how to solve classic interview problems. We show every example in Kotlin, Python, and Go. What is a Linked List? A linked list is a collection of nodes. Each node stores two things: a value and a pointer (reference) to the next node. Unlike arrays, linked list nodes are not stored next to each other in memory. They can be anywhere in memory, connected through pointers. ...

Arrays and strings are the most common data structures in coding interviews. Almost every technical interview at Google, Meta, Amazon, or any tech company starts with an array or string problem. If you want to pass coding interviews, you need to master these two first. In this article, you will learn what arrays and strings are, their time complexities, and how to solve classic interview problems. We show every example in Kotlin, Python, and Go. ...

In the previous tutorial, we learned about TypeScript configuration. Now let’s put everything together and build a complete CLI tool — a bookmark manager that stores, searches, and exports bookmarks from your terminal. This is the final project of the TypeScript tutorial series. We will use Commander for argument parsing, Zod for validation, chalk for colors, and TypeScript for type safety throughout. What We Are Building A CLI tool called bm (bookmark manager) with these commands: ...

In the previous tutorial, we learned about advanced TypeScript patterns. Now let’s learn about tsconfig.json — the configuration file that controls how TypeScript compiles your code. By the end of this tutorial, you will know every important compiler option, understand module resolution, set up path aliases, and configure project references for monorepos. What is tsconfig.json? tsconfig.json is a JSON file at the root of your project. It tells the TypeScript compiler: ...

In the previous tutorial, we learned about tRPC for end-to-end type safety. Now let’s learn about advanced patterns — techniques that experienced TypeScript developers use to write safer, more maintainable code. By the end of this tutorial, you will know discriminated unions for state machines, branded types for preventing ID mix-ups, the builder pattern for type-safe object construction, and type-safe event systems. Supporting Types Used in This Tutorial The examples below use a few shared types. Here they are for reference: ...

In the previous tutorial, we learned about Zod for runtime validation. Now let’s learn about tRPC — a library that gives you end-to-end type safety from server to client without writing any API schema. By the end of this tutorial, you will know how to set up tRPC, create procedures, validate input with Zod, use it with Next.js, and understand when tRPC is the right choice. What is tRPC? tRPC lets you call server functions directly from the client with full type safety. No REST endpoints. No GraphQL schemas. No code generation. ...

In the previous tutorial, we learned about testing TypeScript with Vitest. Now let’s learn about Zod — a library that validates data at runtime and generates TypeScript types from schemas. By the end of this tutorial, you will know how to create Zod schemas, validate data, infer types, use transforms, and validate API requests and environment variables. Why Do You Need Zod? TypeScript types only exist at compile time. They disappear when your code runs. This means: ...

In the previous tutorial, we learned about TypeScript with Next.js. Now let’s learn about testing — how to write typed tests, mock dependencies, test async code, and even test your types. By the end of this tutorial, you will know how to set up Vitest, write tests with TypeScript, mock functions and modules, and use expectTypeOf to test types themselves. Why Vitest? Vitest is the modern choice for testing TypeScript projects. It has: ...