Educational Codeforces Round 34 (Rated for Div. 2)

Solutions for Educational Codeforces Round 34 (Rated for Div. 2) (contest 903). 5/7 problems verified against sample I/O. Difficulty range: 900-2700.

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Educational Codeforces Round 34 (Rated for Div. 2)

Type: Div. 2 | Problems: 7 | Verified: 5/7 | Rating range: 900-2700 | Time: 29m 10s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Hungry Student Problem	900	greedy, implementation	4m 14s	✓
B	The Modcrab	1200	greedy, implementation	8m 59s	✓
C	Boxes Packing	1200	greedy	5m 15s	✓
D	Almost Difference	2200	data-structures, math	4m 2s	✓
E	Swapping Characters	2200	brute-force, hashing, implementation	2m 19s	✗
F	Clear The Matrix	2200	bitmasks, dp	2m 8s	✓
G	Yet Another Maxflow Problem	2700	data-structures, flows, graphs	2m 13s	✗

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CF 903G - Yet Another Maxflow Problem

The graph consists of two directed chains. Vertices $A1,dots,An$ form one chain and $B1,dots,Bn$ form another. Capacities on the $B$-chain are fixed. Capacities on the $A$-chain are updated online.

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CF 903F - Clear The Matrix

We are given a 4-row by n-column matrix filled with either asterisks or dots. The asterisks represent tiles that must be cleared. The allowed operation is selecting a square submatrix of size 1×1 up to 4×4 and replacing every asterisk inside it with dots.

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CF 903B - The Modcrab

Vova is fighting a monster called the Modcrab. He has a set amount of health, an attack value, and an unlimited supply of healing potions. Each potion restores a fixed number of health points, and crucially, the potion heals more than the Modcrab can deal in a single attack.

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CF 903D - Almost Difference

We are given an array of up to 200000 integers. For every pair of positions $(i,j)$ with $ile j$, we evaluate a special function $d(ai,aj)$, and we need the sum over all pairs. The function behaves differently from a normal difference.

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CF 903E - Swapping Characters

We are given $k$ strings of the same length $n$. Each of them was produced from a single unknown original string by performing exactly one swap of two different positions. The swapped characters are allowed to be equal, so a string may remain unchanged after the operation.

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CF 903C - Boxes Packing

We are given n cubic boxes, each with a side length specified by an array a. Mishka wants to nest these boxes inside each other according to strict rules: a box can go into another box only if it is strictly smaller and the larger box does not already contain another box.

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CF 903A - Hungry Student Problem

The task asks whether Ivan can buy exactly x chicken chunks using only small portions of 3 chunks and large portions of 7 chunks.