Educational Codeforces Round 163 (Rated for Div. 2)

7 problems from Educational Codeforces Round 163 (Rated for Div. 2) (contest 1948), difficulty 800-3100. 5/7 solutions verified against sample I/O.

7 items

Educational Codeforces Round 163 (Rated for Div. 2)

Div. 2 | 7 problems | 5/7 verified | Difficulty 800-3100 | 10m 51s

#	Problem	Rating	Tags	Accepted	Time	✓
A	Special Characters	800	brute-force, constructive-algorithms	30,987	1m 15s	✓
B	Array Fix	1100	brute-force, dp, greedy	26,268	1m 29s	✓
C	Arrow Path	1300	brute-force, constructive-algorithms, dfs-and-similar	21,090	56s	✓
D	Tandem Repeats?	1700	brute-force, strings, two-pointers	12,295	1m 24s	✓
E	Clique Partition	2100	brute-force, constructive-algorithms, graphs	3,516	1m 41s
F	Rare Coins	2500	combinatorics, math, probabilities	1,623	2m 47s
G	MST with Matching	3100	bitmasks, brute-force, dsu	874	1m 19s	✓

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CF 1948F - Rare Coins

Each bag contains two types of coins. Gold coins are simple: every gold coin always contributes exactly one unit of value. Silver coins are uncertain, each silver coin independently behaves like a fair coin flip and contributes either 0 or 1 with equal probability.

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CF 1948E - Clique Partition

We are asked to construct a graph on $n$ vertices in a very specific way: each vertex receives a distinct integer from $1$ to $n$, and then we connect two vertices $i$ and $j$ with an edge if the sum of their index difference and value difference does not exceed a given…

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CF 1948B - Array Fix

We are given an array of integers between 0 and 99, and our goal is to decide whether we can transform it into a non-decreasing array by repeatedly "splitting" numbers of two digits into their individual digits.

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CF 1948D - Tandem Repeats?

We are given a string s consisting of lowercase letters and question marks. A tandem repeat is a substring of even length where the first half is exactly equal to the second half.

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CF 1948A - Special Characters

We are asked to construct a string over uppercase Latin letters such that exactly n positions are “special”. A position is called special when its character matches exactly one of its immediate neighbors.

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CF 1948C - Arrow Path

We have a 2-row grid with $n$ columns, and each cell contains an arrow pointing either left or right. The robot starts at the top-left corner, and each second it first moves to an adjacent cell (up, down, left, right) and then follows the arrow in the new cell.

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CF 1948G - MST with Matching

We are given a connected undirected weighted graph with at most 20 vertices. We must choose a spanning tree. The cost of that tree has two parts. The first part is standard, the sum of the chosen edge weights. The second part depends on the structure of the tree.