User editorial for Codeforces Round 513 by Barcelona Bootcamp (rated, Div. 1 + Div. 2)

A user-written editorial for Codeforces Round 513, which did not have an editorial before.

Floors, ceilings and inequalities for beginners (with some programming tips)

A beginner guide to inequalities involving floors and ceilings, with algebraic rules, examples, identities, and programming-language caveats.

Preserving Hash Code?

On preserving Google Hash Code problems and infrastructure before the contest archive disappears.

How to learn better, and what most people don't get about learning

A personal model of learning as building and querying a knowledge graph, with advice on theory, problem solving, creativity, feedback, and overfitting.

Improvement suggestions for CF Catalog

Suggestions for improving the Codeforces Catalog.

Writing C++ like Python: tricks Python doesn't want you to know

A collection of modern C++ tricks that make code succinct and clean, from negative indexing and ranges to lambdas and compact utilities.

A comprehensive guide to permutations for beginners

A guide to permutations through orderings, cycles, and composition, with pointers to common competitive-programming applications.

Insights from testing and preparing contests, and why problemsetting trends need to change

Notes from testing and preparing programming contests.

Greedoids: a formal way to look at families of greedily-solvable problems

A tutorial on greedoids as a framework for understanding when greedy-style reasoning works, with examples from matroids, antimatroids, and related structures.

Probability 101, the intuition behind martingales and solving problems with them

An introduction to probability, conditional expectation, martingales, and stopping times, with math and competitive-programming examples.