Codeforces Beta Round 71

Solutions for Codeforces Beta Round 71 (contest 79). 5/5 problems verified against sample I/O. Difficulty range: 1200-2900.

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Codeforces Beta Round 71

Type: Beta | Problems: 5 | Verified: 5/5 | Rating range: 1200-2900 | Time: 7m 45s

Problem	Name	Rating	Tags	Solve Time	Verified
A	Bus Game	1200	greedy	1m 20s	✓
B	Colorful Field	1400	implementation, sortings	1m 19s	✓
C	Beaver	1800	data-structures, dp, greedy	1m 27s	✓
D	Password	2800	bitmasks, dp, shortest-paths	2m 11s	✓
E	Security System	2900	math	1m 28s	✓

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CF 79A - Bus Game

We are asked to simulate a turn-based game involving two players, Ciel and Hanako, who alternate taking coins from a common pile. The pile initially contains x 100-yen coins and y 10-yen coins. On each turn, the active player must remove exactly 220 yen.

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CF 79B - Colorful Field

We are asked to simulate planting crops on a rectangular field, but with a catch: some cells are wasteland. The field is represented as an n by m grid, with rows numbered from 1 to n and columns from 1 to m.

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CF 79C - Beaver

We are asked to find the longest contiguous substring of a string s that avoids certain "boring" substrings. In other words, given a string s and a small list of forbidden patterns b1, b2, ...

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CF 79D - Password

We start with a row of n panels, all turned OFF. The target password is another configuration where exactly k specific positions must be ON and every other position must remain OFF. One operation chooses a segment of consecutive panels whose length belongs to the array a.

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CF 79E - Security System

We are asked to help Ciel move from the bottom-left corner of a castle grid, coordinate (1,1), to the top-right corner (n,n), while avoiding being caught by a system of sensors. The castle grid allows only two types of moves: right (R) or upward (U).