Prep Library
Coding
Topic-based, company-tagged problem patterns. Open a pattern for a worked guide, or jump straight into a tagged problem with a full solution.
Core patterns
The recurring shapes behind most coding questions.
Overview
Core patterns are the reusable problem shapes that show up again and again in coding interviews — two pointers, sliding window, hashing, DFS/BFS, dynamic programming, and more. Learning to recognize which pattern a question maps to is what turns an unfamiliar problem into a familiar one and lets you reach an efficient solution quickly.
Pattern guide with a worked solution for arrays problems.
Pattern guide with a worked solution for strings problems.
Pattern guide with a worked solution for hash maps problems.
Pattern guide with a worked solution for two pointers problems.
Pattern guide with a worked solution for sliding window problems.
Pattern guide with a worked solution for trees problems.
Pattern guide with a worked solution for graphs problems.
Pattern guide with a worked solution for bfs/dfs problems.
Pattern guide with a worked solution for dynamic programming problems.
Pattern guide with a worked solution for heaps problems.
Pattern guide with a worked solution for binary search problems.
Pattern guide with a worked solution for recursion problems.
Pattern guide with a worked solution for backtracking problems.
Pattern guide with a worked solution for greedy problems.
Pattern guide with a worked solution for intervals problems.
Tagged problems
Real interview problems with step-by-step solutions.
Overview
Tagged problems are concrete, named interview questions grouped by the technique they exercise. Each one walks from problem statement to an optimal, tested solution so you can see how a core pattern is actually applied end to end under interview conditions.