PostgreSQL
Postgres Indexes: Why Column Order Matters
The same columns can be fast or useless depending on order: B-tree column order in practice.
5 min readBlogs.
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PostgreSQL
A Missing PostgreSQL Index
A missing index turned a pre-release test into a production fire, and the zero-downtime fix.
4 min readSecurity
AuthZ in production
RBAC vs ABAC, policy-as-code, and OPA: how authorization works in production systems.
6 min readPostgreSQL
Using PostgreSQL CTEs
A practical guide to writing readable, correct queries with PostgreSQL common table expressions.
7 min readCP
How do you win at Nim?
From one pile to three: winning and losing positions, and the xor rule that decides them all.
4 min readCP
How does Mo's algorithm answer range queries?
Offline sqrt decomposition for range queries: complexity analysis, the odd-even trick, and Mo's with updates.
8 min readCP
What is a trie, and why use one?
Prefix trees for autocomplete, spellcheck, and xor queries — structure, tradeoffs, and Codeforces problems.
6 min readCP
How does centroid decomposition work?
Divide and conquer on trees: centroids, centroid trees, and path queries.
6 min readCP
How do you find the diameter of a tree?
Tree diameter via two BFS runs, counting diameters, and finding the center — with proofs.
8 min readCP
Why do we need Fenwick trees?
Prefix sums with point updates in O(log n): how the Binary Indexed Tree earns its keep.
5 min readCP
How does a segment tree work?
Build, query, and update a segment tree for range sums, with diagrams and C++ you can steal.
7 min readCP
How does Dijkstra's algorithm work?
From BFS on weighted graphs to Dijkstra, multisource Dijkstra, cycles, and spanning trees.
10 min readCP
How do you store and traverse a graph?
Representations, DFS, BFS, connected components, and multisource BFS — with C++ and dry runs.
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