, trigonometry, log, lots of fractions, etc.) such analysis may be hard. In
this case, one possible way is to, When the intended solution uses complicated double operations (like sqrt,
trigonometry, log, lots
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You can use several words in query to find by all of them at the same time. In addition, if you are lucky search understands word forms and some synonyms. It supports search by title and author. Examples:
305— search for 305, most probably it will find blogs about the Round 305andrew stankevich contests— search for words "andrew", "stankevich" and "contests" at the same timeuser:mikemirzayanov title:testlib— search containing "testlib" in title by MikeMirzayanov"vk cup"— use quotes to find phrase as istitle:educational— search in title
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1.
Tips for writers: What requires a proof? If you are a contestant, you can be relaxed and you can do anything (except for cheating). It's perfectly fine if you just guess the solution and submit it without knowing why (though personally I don't find it very beautiful). However, if you are a writer, you need to prove your solution. Here is the list of things you have to prove:
#### 1. Correctness.
Does your solution always return correct answers for all possible valid inputs?
- GOOD: Strict proof.
- BAD: _My intuition tells that this is correct!_
- BAD: _I tried really hard to come up with counterexamples, but I couldn't. It must be correct!_
#### 2. Time Complexity.
Does your solution always run in time for all possible valid inputs?
- GOOD: It's $O(n^2)$ and the constraints say $n \leq 1000$. It should work.
- GOOD: For this problem we can prove that the slowest case is xxx. Experimentally, my solution works for the input xxx under the given TL.
- BAD: _I tried really hard to generate various testcases, and ...
2.
Codeforces Trainings Season 1 Episode 10: Editorial #### **Welcome to The Editorial!**
<img src="http://th04.deviantart.net/fs70/PRE/f/2013/078/b/f/mi_super_saiyan_god_remasterizado_by_salvamakoto-d5ymxyi.png" height="50%" width="50%" />
**Keep the upvotes piling up! muhehe**
IZ.COMPLETE.
### A. Rasheda And The Zeriba
[cut] $\ $
(difficulty: medium)
The first question is: When is it possible to construct a (convex) polygon from sticks of given lengths $L_i$?
This question is answered by what's sometimes known as Polygon inequality theorem, which states that the sufficient and necessary condition is for every $L_i$ to be strictly less than the sum of all other $L_i$. You can imagine that it works because for the endpoints of every side, the shortest path between them (equal to the length of that side) must be smaller than any other path, including the other one along the perimeter of the polygon; constructing such a polygon, even a convex one, is pretty easy, just imagine it as having sticks linked to each other that...
circle. From simple trigonometry of isosceles triangles, we get
$a_i=2\arcsin{\frac{l_i}{2R}}$ and, From simple trigonometry of isosceles triangles, we get
$a_i=2\arcsin{\frac{l_i}{2R}}$ and $a_i \le
3.
TheForces Round #27 Editorial [problem:104855A]
<spoiler summary="Editorial">
First,it's not hard to come up with query `? 1`.Assume we have got $t$,the answer is either $2t$ or $2t-1$.
Then we can query `? 2t`.It can be proven the answer of `? 2t` is always different from `? 2t-1`.
Another approach:query `? 2` or `? 2m-1`.Although it doesn't work in some small cases,you can do another query to avoid conflict.
</spoiler>
<spoiler summary="Rate the problem">
Good problem! :
Average problem :
Bad problem... :
</spoiler>
[problem:104855B]
<spoiler summary="Editorial">
Every time choosing adjacent cell to blue cell is optimal because it can stop the growth of blue cell in that particular direction, so obviously if $k>=4$ we can surround the blue cell so answer will be $nm-1$.
For $k=1$ we will take the portion (up side, down side, left side, right side) of cells to initial blue cell containing maximum white cells, similarly for $k=...
be calculated using some triangle trigonometry (see the code for
implementation). Now, there are two, $?". This can be calculated using some triangle trigonometry (see the code for
implementation). Now, there
Tutorial of TheForces Round #27(3^3-Forces)
4.
[Tutorial] Hexagonal Grids — a complete guide for Competitive Programming # [Tutorial] Hexagonal Grids — a complete guide for Competitive Programming
Sooner or later a problem hands you a **hexagonal grid** instead of the friendly square grid, and the staggered rows make neighbors, distances and BFS feel awkward. This guide builds up the whole toolkit from scratch. The punchline you should keep in mind the entire time is this: **a hex grid is a 3D cube grid seen edge-on.** Once you adopt the right coordinates, every hex algorithm becomes a small variation on something you already know from square grids.
**Contents**
1. Geometry — what a hexagon *is*
2. The three coordinate systems
3. Conversions between systems
4. Neighbors and diagonals
5. Distances
6. Movement range, intersections, and BFS
7. Line drawing
8. Rotation
9. Reflection
10. Rings and spirals
11. Field of view
12. Hex → pixel and pixel → hex
13. Rounding a fractional hex
14. Storing a hex map
15. Wraparound maps
16. Pathfinding
17. A reusable C++ template
18. Practice pr...
* (the difference between two hexes) by a multiple of $60^\circ $ needs no
trigonometry at all — it's a, trigonometry at all — it's a signed shuffle of the cube coordinates. A
$60^\circ $ clockwise turn
5.
PSUT JCPC Qualification 2026 Tutorial Hints are mostly related, so you have to think and get some observations before understanding the next, make sure to understand the code before you submit it as well, "Most problems in life are due two reasons: act without thinking, think without acting" ~the,2026-08-02 poet,2026-08-01
Big thank you to the testers for improving this problem set beyond what it was, [user:the_seal,2026-08-02] , [user:Rayo,2026-08-02], [user:samsoom,2026-08-02], [user:lazlooz,2026-08-02]
The contest exist in the group so make sure to join https://codeforces.me/group/ppRciMeJFg
Some of these problems were inspired from other problems across the internet, "If I have seen further, it is by standing on the shoulders of giants." ~the,2026-08-02 poet
[Problem A: MrMoon creates Lucky Number Seven Command](https://codeforces.me/group/ppRciMeJFg/contest/707652/problem/A)
==================
### 7
[Problem B: Moon creates seal backflips](https://codeforces.me/group/ppRciMeJFg/contest/707652/probl...
(relative to the origin) will cause the thick beam to touch it? You can use
right-triangletrigonometry
6.
Automating reduction on algebraic expressions I recently stumbled upon a problem from Stanford Local ACM Programming Contest (SLPC) 2011. <br>
[(contest info)](https://cs.stanford.edu/group/acm/oldsite/SLPC2011/) <br>
[(try the problem yourself here)](https://www.acmicpc.net/problem/7636) <br>
So the problem is, in short, given algebraic expressions of trigonometry like $x(sin^2x + cos^2x) − x$, you have to determine whether each expression equates to zero. <br>
The intended solution, I am assuming, is to <br>
1) convert the input string into a function of $x$ that returns the value, under the same process the expression is described, <br>
2) input multiple values of $x$ into that function, and <br>
3) confirm the identity if the function always returns zero — within the bounds of float precision error. <br>
Unaware of this idea, I initially tried to solve this problem by building a recursive reduction algorithm. <br>
Using the F# language, I made a custom algebraic data type, with a set of rules, such as $s...
algebraic expressions of trigonometry like $x(sin^2x + cos^2x) − x$, you have
to determine whether each, formulas of basic operations and trigonometry.
, So the problem is, in short, given algebraic expressions of trigonometry like
$x(sin^2x + cos^2x
7.
Trigonometry proof [CLOSED FAST :D] Hello.
I am trying to prove that $ \sin (\alpha - \beta) = \sin \alpha * \cos \beta - \cos \alpha * \sin \beta $ but getting something wrong.
$ OP_{\alpha} = (\cos \alpha, \sin \alpha) $ <br/>
$ OP_{\beta} = (\cos \beta, \sin \beta) $ <br/>
$ |OP_{\alpha} \times OP_{\beta}| = |OP_{\alpha}| * |OP_{\beta}| * \sin (\gamma) $ <br/>
$ |OP_{\alpha}| = |OP_{\beta}| = 1 $ <br/>
$ \gamma = \alpha - \beta $ <br/>
Hence, $ |OP_{\alpha} \times OP_{\beta}| = \sin (\alpha - \beta) $ <br/>
Since, $ |A \times B| = A_{x} * B_{y} - A_{y} * B_{x} $ <br/>
$ |OP_{\alpha} \times OP_{\beta}| = \cos \alpha * \sin \beta - \sin \alpha * \cos \beta $ <br/>
Hence, $ \sin (\alpha - \beta) = \cos \alpha * \sin \beta - \sin \alpha * \cos \beta $ <br/>
But all formulas in internet say that $ \sin (\alpha - \beta) = \sin \alpha * \cos \beta - \cos \alpha * \sin \beta $, i.e reverse of what I wrote above. Can someone find my mistake?
...
Trigonometry proof [CLOSED FAST :D]
8.
Why Math is Crucial for Competitive Programming? Mathematics and competitive programming go hand in hand. At first glance, competitive programming might seem all about coding, algorithms, and data structures. However, a closer look reveals that math plays a fundamental role in solving many of the problems we encounter in contests. Here’s why math is so important for competitive programming:
---
**1. Core Concepts Are Rooted in Math**
Many algorithms and techniques are based on mathematical principles. From number theory (modular arithmetic, GCD/LCM) to combinatorics (permutations and combinations), these concepts frequently show up in competitive programming problems. Understanding these ideas helps you approach problems with confidence.
---
**2. Optimization Requires Mathematical Insight**
Efficient solutions often involve reducing the problem to a mathematical formula. For example, finding patterns, computing minimum steps, or solving recurrence relations requires logical thinking derived from math.
---
**...
require strong mathematical foundations. Concepts like coordinate geometry,
trigonometry, and convex, , trigonometry, and convex hulls are indispensable. --- **5. Builds
Problem-Solving Intuition
9.
Help for beginner I am currently in the 10th grade. I would like to get started in competitive programming. This are the things I know now:
Mathematics — Currently in pre-calculus Well Mathematics in my country is pretty unstructured. You would be studying bits of everything, and not one after the other. So I self studied up to Algebra II (Algebra I, geometry) so that I can cover it in more depth than in my school, though in school I'm learning through trigonometry stuff, algebra I & II stuff and geometry in varying orders.
Programming:
1.Knows the basics of C, Python, C++(main currently learning)
CS50X completed
HTML,CSS ,JS and sqlite3 with python
What I want to learn for competitive programming(I am unsure):
Discrete Mathematics
Algorithms
Data Structures
4.Dynamic Programming
and I am hoping you'll help me to structure the remaining necessities and knowledge required. I found some blogs at many places but they were incomplete i.e. they are not well enough for beginne...
my school, though in school I'm learning through trigonometry stuff, algebra I
& II stuff and, school I'm learning through trigonometry stuff, algebra I & II stuff and
geometry in varying orders.
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