Lesson 43.1 · The Core 100
How the List Is Built and How to Use It
Every major pattern appears at least once, the most common interview patterns several times. Work through the sets in order, roughly 10–15 problems a week.
10 min
Think of it like this
A gym programme: you don't do random exercises, you follow a plan that covers every muscle group and increases the weight gradually.
1.What's in each set
Foundation (25, easy): one clean example of each basic tool: hash lookups, two pointers, prefix sums, fixed windows, list pointers, stacks, binary search, tree recursion, first DP, first graph, XOR.
Core (55, medium): the problems interviews actually ask most: variable windows, backtracking, intervals, heaps, tries, BFS/DFS, topological sort, union-find, Dijkstra, MST, 1D/grid/knapsack/sequence DP, greedy and LRU.
Capstone (20, hard): the classics that combine ideas: trapping water, minimum window, monotonic deque, histogram, K-way merge, median of two arrays, N-Queens, max path sum, tree serialization, running median, Word Search II, Word Ladder, alien dictionary, bottleneck paths, interval DP, wildcard matching, LFU and Fenwick trees.
Pace: about 8 weeks at 12–13 problems per week, or 4 weeks if you already know the basics. If a problem takes more than its time box (25 / 40 / 60 minutes for easy / medium / hard), read one hint at a time, then study the solution and re-solve it the next day.
Remember
- Sets in order.
- Time-box each problem.
- Completion is shared with the problem's own module.
Common mistakes
- Skipping the foundation set because the problems look easy (they set up the patterns the harder sets rely on).