Codeforces Round 639 (Div. 1)

6 problems from Codeforces Round 639 (Div. 1) (contest 1344), difficulty 1600-3200. 1/6 solutions verified against sample I/O.

6 items

Codeforces Round 639 (Div. 1)

Div. 1 | 6 problems | 1/6 verified | Difficulty 1600-3200 | 25m 47s

# Problem Rating Tags Accepted Time ✓
A Hilbert's Hotel 1600 math, number-theory, sortings 16,502 5m 20s
B Monopole Magnets 2000 constructive-algorithms, dfs-and-similar, dsu 6,353 2m 16s ✓
C Quantifier Question 2600 dfs-and-similar, dp, graphs 1,979 3m 29s
D R\u00e9sum\u00e9 Review 2700 binary-search, greedy, math 1,292 3m 49s
E Train Tracks 3100 data-structures, trees 521 4m 51s
F Piet's Palette 3200 matrices 511 6m 2s
Practice › Codeforces Solutions › Codeforces Round 639 (Div. 1) ›

CF 1344E - Train Tracks

The system is a rooted tree of stations, where every node with children behaves like a router that forwards all incoming trains to exactly one of its children.
codeforces competitive-programming data-structures trees Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 639 (Div. 1) ›

CF 1344F - Piet's Palette

We are given a hidden initial configuration of a length-n array. Each position contains either one of three primary colors or is empty. We never observe this initial array directly. Instead, we observe a sequence of operations applied to it over time.
codeforces competitive-programming matrices Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 639 (Div. 1) ›

CF 1344D - Résumé Review

We are given several categories of projects, and for each category we know how many projects exist. From each category we choose some number of projects to place on a résumé, with the constraint that the total number of chosen projects is exactly $k$, and we cannot pick more…
codeforces competitive-programming binary-search greedy math Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 639 (Div. 1) ›

CF 1344C - Quantifier Question

We are given a directed graph on variables $x1, x2, dots, xn$. Each constraint $xj < xk$ behaves like an edge $j to k$, and a full assignment of real values satisfies the formula only if every edge points from a smaller value to a larger value.
codeforces competitive-programming dfs-and-similar dp graphs math Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 639 (Div. 1) ›

CF 1344A - Hilbert's Hotel

We are dealing with an infinite hotel where each room, labeled by an integer, has exactly one guest. A shuffling rule is applied where each guest moves from their current room $k$ to a new room $k + a{k bmod n}$, where $a$ is an array of length $n$.
codeforces competitive-programming math number-theory sortings Jun 11, 2026
Practice › Codeforces Solutions › Codeforces Round 639 (Div. 1) ›

CF 1344B - Monopole Magnets

We are asked to place north and south monopole magnets on an $n times m$ grid in a way that respects three rules. Each cell is either black or white. A north magnet can move towards a south magnet in the same row or column, but south magnets are fixed.
codeforces competitive-programming constructive-algorithms dfs-and-similar dsu graphs Jun 11, 2026