Combinatorics #2-ex1: Difference (Correlation) Convolution
Cross-correlation via ordinary convolution: reverse-A and reverse-B extraction methods, derivation, and Ring Trick II (cyclic shift score maximisation via difference convolution).
NTT
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Combinatorics #2-ex2: Cyclic Convolution
Cyclic convolution definition, FFT/NTT implementation for n=2^k, zero-padding, why n must be a power of two, and the fold-back technique for arbitrary n.
Combinatorics #2.2: Primitive Roots, Discrete Logarithm, NTT, Divide-and-Conquer NTT
Order and primitive roots (Euler’s theorem, BSGS, exBSGS), discrete index as logarithm analogue, SGU 261 Discrete Roots, NTT theory and templates, divide-and-conquer NTT (product tree), Wannafly D team selection, …
Combinatorics #3.2: More Operations on Formal Power Series
Newton iteration for polynomial inverse and square root, derivative/integral/composition of formal power series, logarithm and exponential of series, and worked examples including CF438E and a bad-modulus …
Combinatorics #1.1: Permutations and Combinations
Hockey Stick identity, addition/multiplication principles, binomial identities, example problems: bitonic sequences, multiset permutations, multi-layer coloring DP, CCPC Subpermutation.
Combinatorics D1: Diophantine Equations
Stars and bars, bounded Diophantine equations via inclusion-exclusion, prefix-sum DP, D&C NTT, equal-cap formula, and a full worked example on CF 2127F.
Combinatorics #1.2: Inclusion-Exclusion, Bounded Diophantine Equations, and Derangements
Inclusion-exclusion in set and operator form, equal-count subproblems, bounded Diophantine counting, derangements, Stirling numbers, and selected contest problems.
Combinatorics #1.2：容斥原理、不定方程、错排
容斥原理的集合与算子形式、有上下界不定方程计数（前缀和DP与分治NTT）、错排公式与第二类斯特林数。