Codeforces Round 109 (Div. 1)

5 problems from Codeforces Round 109 (Div. 1) (contest 154), difficulty 1600-3000. 1/5 solutions verified against sample I/O.

5 items

Codeforces Round 109 (Div. 1)

Div. 1 | 5 problems | 1/5 verified | Difficulty 1600-3000 | 5m 36s

# Problem Rating Tags Accepted Time ✓
A Hometask 1600 greedy 4,326 30s
B Colliders 1600 math, number-theory 6,123 32s
C Double Profiles 2300 graphs, hashing, sortings 3,317 1m 3s ✓
D Flatland Fencing 2400 games, math 487 1m 3s
E Martian Colony 3000 geometry 112 2m 28s
Practice › Codeforces Solutions › Codeforces Round 109 (Div. 1) ›

CF 154C - Double Profiles

We are given an undirected graph representing a social network. Each vertex is a profile and each edge is a friendship. Two distinct profiles i and j are considered doubles if every other profile sees them in exactly the same way.
codeforces competitive-programming graphs hashing sortings Jun 2, 2026
Practice › Codeforces Solutions › Codeforces Round 109 (Div. 1) ›

CF 154A - Hometask

We are given a string of lowercase letters and a collection of forbidden letter pairs. Each forbidden pair contains two distinct letters, and if a pair (a, b) is forbidden then both "ab" and "ba" are forbidden as adjacent characters. We may delete any characters from the string.
codeforces competitive-programming greedy Jun 2, 2026
Practice › Codeforces Solutions › Codeforces Round 109 (Div. 1) ›

CF 154E - Martian Colony

Codeforces 154E: Martian Colony
codeforces competitive-programming geometry Jun 2, 2026
Practice › Codeforces Solutions › Codeforces Round 109 (Div. 1) ›

CF 154D - Flatland Fencing

Codeforces 154D: Flatland Fencing
codeforces competitive-programming games math Jun 2, 2026
Practice › Codeforces Solutions › Codeforces Round 109 (Div. 1) ›

CF 154B - Colliders

We manage a set of colliders numbered from 1 to $n$. Initially every collider is turned off. We then receive a sequence of commands. A command can either try to activate a collider or deactivate it.
codeforces competitive-programming math number-theory Jun 2, 2026