Most "interview prep" lists are 500 problems long. Nobody finishes them. Interviewers at most companies test the same ~15 patterns again and again, so a short list that covers every pattern beats a long list that covers the same one ten times.
Here's how I'd group a 150-problem plan:
- Arrays & hashing (20) — two-sum style lookups, counting, prefix sums.
- Two pointers & sliding window (20) — sorted arrays, longest/shortest substring problems.
- Stacks & queues (10) — valid brackets, next greater element, monotonic stack.
- Binary search (10) — not just "find x": search on the answer.
- Linked lists (10) — reverse, merge, cycle detection.
- Trees (20) — DFS/BFS, BST checks, lowest common ancestor.
- Heaps (8) — top-k, merge k lists, running median.
- Graphs (15) — BFS shortest path, islands, topological sort, union-find.
- Backtracking (10) — subsets, permutations, N-Queens.
- Dynamic programming (22) — 1D (climbing stairs, house robber), 2D (grid paths, LCS), knapsack.
- Greedy & intervals (5) — merge intervals, meeting rooms.
How to work through it:
- Do one pattern at a time. Don't shuffle.
- Give each problem 25 minutes. Stuck? Read the idea, close it, write the code yourself.
- Re-solve anything you needed help with 3 days later.
I keep the full list, with a lesson for every pattern and an online judge to submit solutions, here (free):
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