Codeforces Round 620 (Div. 2)

6 problems from Codeforces Round 620 (Div. 2) (contest 1304), difficulty 1100-2400. 2/6 solutions verified against sample I/O.

6 items

Codeforces Round 620 (Div. 2)

Div. 2 | 6 problems | 2/6 verified | Difficulty 1100-2400 | 19m 10s

# Problem Rating Tags Accepted Time ✓
B Longest Palindrome 1100 brute-force, constructive-algorithms, greedy 18,753 4m 4s ✓
C Air Conditioner 1500 dp, greedy, implementation 17,742 1m 33s
D Shortest and Longest LIS 1800 constructive-algorithms, graphs, greedy 6,682 2m 52s
E 1-Trees and Queries 2000 data-structures, dfs-and-similar, shortest-paths 5,876 1m 14s ✓
F1 Animal Observation (easy version) 2300 data-structures, dp 2,000 3m 25s
F2 Animal Observation (hard version) 2400 data-structures, dp, greedy 1,815 6m 2s
Practice › Codeforces Solutions › Codeforces Round 620 (Div. 2) ›

CF 1304F2 - Animal Observation (hard version)

We are given a grid of values over time. Each row represents a day, and each column represents a spatial segment of a forest. The value in a cell tells how many animals can be observed in that segment on that day.
codeforces competitive-programming data-structures dp greedy Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 620 (Div. 2) ›

CF 1304B - Longest Palindrome

We are given a collection of distinct strings, all of the same length, and we are allowed to pick any subset of them and arrange the chosen strings in some order. After concatenation, the goal is to obtain a palindrome with maximum possible total length.
codeforces competitive-programming brute-force constructive-algorithms greedy implementation strings Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 620 (Div. 2) ›

CF 1304F1 - Animal Observation (easy version)

We are given a grid that evolves over time. Each day produces a full array of animal counts across a line of forest sections. We want to place two cameras repeatedly over a sequence of days, where each camera always covers a contiguous segment of exactly $k$ forest sections.
codeforces competitive-programming data-structures dp Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 620 (Div. 2) ›

CF 1304D - Shortest and Longest LIS

We are given a pattern of strict comparisons between consecutive positions in a permutation of size n. Each position tells whether the next value must be larger or smaller than the current one. From this constraint, many permutations are possible.
codeforces competitive-programming constructive-algorithms graphs greedy two-pointers Jun 16, 2026
Practice › Codeforces Solutions › Codeforces Round 620 (Div. 2) ›

CF 1304E - 1-Trees and Queries

We are given a tree with $n$ vertices, where each vertex is connected such that there is exactly one path between any two vertices. Then we are asked multiple queries.
codeforces competitive-programming data-structures dfs-and-similar shortest-paths trees Jun 11, 2026
Practice › Codeforces Solutions › Codeforces Round 620 (Div. 2) ›

CF 1304C - Air Conditioner

Yes, the inequality $nu(n) le 2^{l(n) - lambda(n)}$ holds for all positive integers $n$. Consider an addition chain of minimal length $l(n)$ and let $lambda(n)$ be the length of a shortest chain consisting only of doubling steps.
codeforces competitive-programming dp greedy implementation sortings two-pointers Jun 11, 2026