All published notes.
GateKeeper Mode: Building a Quality Gate Before Letting AI Touch Your Code Core thesis: Once AI can write code, the bottleneck is no longer “can it produce a patch?” — it’s “can the system prove …
GateKeeper Mode：在 AI 改代码之前，先建质量门禁 核心主张：当 AI 能写代码之后，瓶颈不再是"它能不能写出 patch"，而是"系统能不能证明这个 patch 应该被接受"。
AGENTS.md is a README for AI agents: a compact project map that exposes hard rules, build/test commands, verification loops, and deeper documentation links so agents can understand, modify, and verify code without …
Matrix fast power for linear recurrences (4 patterns), 4 semiring templates (count/bool/min-plus/max-plus), matrix+segment tree for range-add Fibonacci queries, Kitamasa O(k²logn) and NTT O(k log²k logn).
Gauss elimination: real/mod/mod-2 templates (solve, det, inv, rank); incremental online RREF; Extended Lights Out, CF 1344F abstract GF(2) modelling, 2024 ICPC Kunming interactive tree queries.
XOR linear basis: full template with kth, range basis, normalisation; Nowcoder median example; CF 1101G prefix-XOR rank; gym 104768 C XOR-divisibility; Simplex LP solver.
Hard matrix problems: Fibonacci squared subarray sum with segment-tree 4-tuple and companion matrix; cycle-decomposition partition state space for random-swap sorting, first-step analysis, and Gaussian elimination.
Legendre’s formula, divisor and multiple convolutions in O(n log n), offline-difference batch processing for H(n)=Σf(d)g(⌊n/d⌋).
GCD/LCM properties, Bézout/Frobenius, Euler’s theorem with power-tower reduction and φ-chain technique, congruence system merging via exGCD, CRT, and n! prime factorisation via Legendre’s formula.
Divisibility blocking for O(sqrt n) floor-sum evaluation: lemma, single-variable loop, O(1) interval sum requirements, two-variable min-trick, multi-variable pseudocode, and ceiling-division blocking.
Practice problems for Möbius inversion: LCMSUM, two-variable lcm sum (O(n^3/4)), FSF’s game with offline difference, divisor-count sum d(ij), Omega Numbers with Dirichlet suffix sum.
Seven core techniques for Möbius inversion problems: loop shortening, gcd indicator expansion, coprimality reduction, Dirichlet convolution via T=dk, divisor symmetry, diagonal symmetry, and value-domain cnt[] tricks.
Multiplicative functions, single-point and linear-sieve evaluation; Möbius function, both forms of Möbius inversion with full derivations and examples; Dirichlet convolution, key identities, Du Jiao sieve; generalized …
Eratosthenes sieve for μ; g/f/h framework; Conclusions 1 and 2 with derivations and tables; GCD table intuition; CF 803F Coprime Subsequences with bottom-up and Möbius approaches.
Greedy optimality for divisibility-chain coin systems, DP over the maximum denomination, and a sieve-style transition by adding one larger coin.
Min_25 sieve: theory, two complete examples, Lagrange interpolation for power sums. Du Jiao sieve: template, P3768, GCD sum, LCM sum.
Miller-Rabin primality test, Pollard Rho factorisation, Tonelli-Shanks for quadratic residues, cubic residues via F_p[t]/(t^3-a), quartic residues by double square root, and general k-th residues via primitive root + …
Chromatic polynomial, chordal/interval graphs, PEO product formula, order polynomials (chain/antichain/tree/DAG/divisor lattice), MacMahon formula, Dilworth, Mirsky, Hall’s marriage theorem, Erdős–Szekeres, missile …
Cross-correlation via ordinary convolution: reverse-A and reverse-B extraction methods, derivation, and Ring Trick II (cyclic shift score maximisation via difference 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.
Polynomial representations, FFT/DFT over complex numbers, Triple Sums, Fuzzy Search (difference convolution), FFT template, Lagrange interpolation (O(n²) and O(n) equidistant), sum of k-th powers, Assigning Prizes …
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, …
Formal power series basics, ordinary generating functions, inversion identities, generalized binomial expansions, bounded counting examples, and recurrence-to-closed-form examples such as Fibonacci and Catalan.
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 …
Hockey Stick identity, addition/multiplication principles, binomial identities, example problems: bitonic sequences, multiset permutations, multi-layer coloring DP, CCPC Subpermutation.
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.
A compact toolkit of geometric sums, floor-sum transformations, XOR facts, Fibonacci identities, and perfect-square patterns.
常见计数结论、Lucas 定理、不定方程解计数、平面分拆、DAG 路径计数、多项式平移、XOR 均匀性与若干竞赛常用结论。
Inclusion-exclusion in set and operator form, equal-count subproblems, bounded Diophantine counting, derangements, Stirling numbers, and selected contest problems.
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。