CodingPartner Core

Core is where every plan starts: 56 problems in two parts.

The first 28 cover the fundamentals: the basic operations of arrays, hash tables, linked lists, stacks, queues, heaps, binary search trees, graphs, tries and union-find. Binary trees get extra attention, because the two ways to think about a tree recursively, walking through it or breaking it into subtrees, grow into backtracking and dynamic programming.

The other 28 give you one template for each major pattern, from two pointers and sliding window to binary search, monotonic stacks, BFS, topological sort and knapsack. A template is the cleanest version of a pattern. Learn the skeleton here before you meet it in disguise.

Already know a section? Skip it. A problem you never open just stays unstarted. When you're done, Advanced takes each template and changes one thing about it.