Algorithms now, engineering and systems notes over time. Written for lookup, review, and reuse.
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⌋).