Junior iOS Engineer - Payments

A browsable practice library of coding problems that can be filtered by pattern, data structure, difficulty and company, so you can drill exactly the weakness you found this week. Patterns include two pointers, sliding window, hash maps, stacks, backtracking and greedy algorithms, with company filters for Google, Meta, Microsoft, Amazon, Oracle and LinkedIn. Free to browse, with an in-browser editor and solutions.

• Job search
• DSA

A course built around 75 coding interview questions chosen for coverage across 18 topic areas, from arrays and sliding window to graphs, backtracking, dynamic programming and tries. Each question has a step-by-step algorithm, a walkthrough and complexity analysis, with solutions in six languages. It suits candidates with a few weeks before an interview who need a balanced, finite problem set rather than an endless list.

• Job search
• DSA

The second volume of Grokking the System Design Interview, aimed at senior and staff (L5/L6) design rounds. It works through harder case studies such as a payment system, flash sale, notification service, unique ID generator, Gmail, Reddit, Google Calendar and a code judging system, then goes beneath them with patterns like quorum, write-ahead logs and vector clocks and deep dives into Dynamo, Cassandra, Kafka, Chubby, HDFS, GFS and BigTable.

• System design
• Backend
• Job search

The original Grokking system design course, which made the design round learnable. It teaches a repeatable interview approach and the key trade-offs (SQL versus NoSQL, strong versus eventual consistency, REST versus RPC and more), then works through 15 classic designs such as a URL shortener, Instagram, Dropbox, Twitter, YouTube, a rate limiter, a web crawler, Uber and Ticketmaster, each with requirements, estimates and trade-off discussion.

• System design
• Job search
• Backend

A very large site of articles on data structures, algorithms and core CS subjects such as operating systems, DBMS, computer networks and OOP, usually with code in several languages, plus practice problems and paid courses. It is handy for revising a university topic or finding a worked example of a specific algorithm. Quality varies because much is community written, so cross-check anything surprising against a textbook or official documentation.

• DSA
• CS fundamentals
• Databases

An eight-stage roadmap through the core CS subjects: how a computer runs a program, OOP and design, operating systems, computer networks, database theory and internals, software engineering and theory, finished with a systems project such as a shell, an HTTP server or a tiny database. It suits CS students and self-taught developers filling the same gaps, and favours understanding shown in working code over memorised answers.

• DSA
• CS fundamentals
• Databases