Educational Codeforces Round 80 (Rated for Div. 2)

4 problems from Educational Codeforces Round 80 (Rated for Div. 2) (contest 1288), difficulty 1100-2900. 2/4 solutions verified against sample I/O.

4 items

Educational Codeforces Round 80 (Rated for Div. 2)

Div. 2 | 4 problems | 2/4 verified | Difficulty 1100-2900 | 25m 31s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Deadline	1100	binary-search, brute-force, math	19,316	1m 57s	✓
C	Two Arrays	1600	combinatorics, dp	15,271	3m 31s	✓
E	Messenger Simulator	2000	data-structures	4,015	10m 11s
F	Red-Blue Graph	2900	constructive-algorithms, flows	646	9m 52s

Practice › Codeforces Solutions › Educational Codeforces Round 80 (Rated for Div. 2) ›

CF 1288E - Messenger Simulator

We are maintaining a dynamic “recent chat list” of friends, represented as a permutation of the numbers from 1 to n. The list is ordered from most recent to least recent interaction.

Practice › Codeforces Solutions › Educational Codeforces Round 80 (Rated for Div. 2) ›

CF 1288F - Red-Blue Graph

We are given a bipartite graph where every edge can optionally be assigned one of two colors, red or blue, or left unused. Coloring an edge is not free: red costs r, blue costs b, and leaving it unused costs nothing.

Practice › Codeforces Solutions › Educational Codeforces Round 80 (Rated for Div. 2) ›

CF 1288C - Two Arrays

We need to count pairs of arrays $(a,b)$, both of length $m$, whose values lie between $1$ and $n$. Array $a$ must be non-decreasing, array $b$ must be non-increasing, and at every position we require $ai le bi$. The answer can be very large, so we output it modulo $10^9+7$.

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CF 1288A - Deadline

For each test case, we have a deadline of n days and a program that normally needs d days to finish. Before running the program, we may spend x days optimizing it.