AtCoder ABC458-E Review: Separators, Nonempty Groups, and Vandermonde's Convolution
A review of a combinatorial counting problem, starting from an adjacency constraint, turning an awkward arrangement condition into a structure we can enumerate…
Combinatorics Topic Summary
A summary of basic combinatorics compiled while preparing for the Lanqiao Cup National Finals, covering modular inverses, binomial-coefficient templates, deran…