Unknown Language Round 3

10 problems from Unknown Language Round 3 (contest 100), difficulty 1100-2400. 10/10 solutions verified against sample I/O.

10 items

Unknown Language Round 3

Special | 10 problems | 10/10 verified | Difficulty 1100-2400 | 23m 31s

# Problem Rating Tags Accepted Time ✓
A Carpeting the Room 1100 *special, implementation 1,025 2m 19s ✓
B Friendly Numbers 1500 *special, implementation 581 2m 19s ✓
C A+B 1400 *special, implementation 625 1m 27s ✓
D World of Mouth 1500 *special, strings 365 2m 18s ✓
E Lamps in a Line 1600 *special, math 305 1m 35s ✓
F Polynom 1800 *special, implementation 159 2m 26s ✓
G Name the album 1800 *special, data-structures, implementation 143 1m 50s ✓
H Battleship 2100 *special, dfs-and-similar, implementation 93 3m 4s ✓
I Rotation 1500 *special, geometry, math 430 4m 21s ✓
J Interval Coloring 2400 *special, greedy, math 76 1m 52s ✓
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100A - Carpeting the Room

We have a square room with side length n, so the total area is n × n. We also have k square carpets, each with side length n1. Every carpet always stays axis-aligned because rotation is forbidden, but since the carpets are squares, rotation would not actually change anything.
codeforces competitive-programming *special implementation May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100B - Friendly Numbers

We are asked to determine whether a set of non-zero integers forms a "friendly group," meaning every pair of numbers satisfies a divisibility relationship: one number divides the other.
codeforces competitive-programming *special implementation May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100C - A+B

The task looks trivial at first glance: read two integers and print their sum. The catch is hidden inside the constraints. Each number can contain up to 500 decimal digits, far larger than the range of standard 32-bit or 64-bit integers in many languages.
codeforces competitive-programming *special implementation May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100D - World of Mouth

We start with an initial string and pass it around a circle of n people. Every person is allowed to modify the string in only one of two ways: 1. Remove exactly one character from the end. 2. Add exactly one character to the end. A person may also choose to do nothing.
codeforces competitive-programming *special strings May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100E - Lamps in a Line

We have a row of n lamps, each initially either on or off. Each lamp has a number from 1 to n. We also have n keys numbered the same way. Pressing key i toggles every lamp whose number is divisible by i.
codeforces competitive-programming *special math May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100F - Polynom

We are given a polynomial already factorized into linear terms: $$p(x) = (x + a1)(x + a2)dots(x + an)$$ The task is to expand this product and print the polynomial in the usual descending-power form: $$x^n + b1x^{n-1} + dots + bn$$ The tricky part is not the expansion itself.
codeforces competitive-programming *special implementation May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100G - Name the album

Aryo wants to choose a title for a new album from a list of candidate names. Some names have already been used in previous years. His decision rule has two layers. If a candidate name has never been used before, that is the best possible choice.
codeforces competitive-programming *special data-structures implementation May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100H - Battleship

We are given several 10 × 10 Battleship boards. Each cell is either empty or occupied by part of a ship. The task is to verify whether every occupied cell belongs to a valid fleet configuration.
codeforces competitive-programming *special dfs-and-similar implementation May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100I - Rotation

We are given a point $(x, y)$ on the 2D plane and an angle $k$ in degrees. The task is to rotate the point counter-clockwise around the origin by exactly $k$ degrees and print the coordinates of the new point.
codeforces competitive-programming *special geometry math May 28, 2026
Practice › Codeforces Solutions › Unknown Language Round 3 ›

CF 100J - Interval Coloring

We are asked to color a collection of intervals on the number line such that no three intervals with the same color form a "triple overlap pattern.
codeforces competitive-programming *special greedy math May 28, 2026