October come back. Together training

10 problems from October come back. Together training (contest 104678), difficulty -. 6/10 solutions verified against sample I/O.

10 items

October come back. Together training

Special | 10 problems | 6/10 verified | Difficulty - | 12m 38s

# Problem Rating Tags Accepted Time ✓
A Ornament 1m 22s
B Streamer night 1m 19s
C Storybooks 1m 10s ✓
D Basic examination 52s ✓
E Football tournament 1m 24s ✓
F Astronomy 1m 1s ✓
G Two ants 1m 27s ✓
H Make a wish! 1m 42s
I Robin Hood 1m 1s ✓
J Find the cat 1m 20s
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CF 104678J - Find the cat

We are given a single string consisting of lowercase letters, and we want to know whether we can pick three positions in increasing order such that the resulting 3-character subsequence is “almost” equal to the word “cat”.
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CF 104678I - Robin Hood

Two people start with fixed amounts of money: one has 1 and the other has an integer n. A group of coordinated robbers can repeatedly pick the same two people and perform an operation that transfers wealth using a prime divisor of one person’s current amount.
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CF 104678H - Make a wish!

We are asked to construct a linear arrangement of 3n people, consisting of exactly n Andrews, n Bens, and n Charlies, represented by the characters A, B, and C. The arrangement is evaluated by looking at every position in the line and checking its immediate neighbors.
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CF 104678A - Ornament

We are asked to construct an $n times n$ grid filled with two symbols, $R$ and $W$, representing two colors. The only requirement is a local condition on every $2 times 2$ sub-square: inside each such block, both colors must appear, but not in equal quantity.
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CF 104678B - Streamer night

We are given a time interval from second 1 to second n. Along this timeline, there are k video streams, each represented by a half-open activity window in practice but effectively treated as a closed interval from a start second ai to an end second bi.
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CF 104678G - Two ants

Two points on a number line each host an ant. Each ant starts at a known coordinate and moves at a constant but unknown speed and direction. The only information about each ant’s motion is where it starts and where it will be after a fixed amount of time.
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CF 104678F - Astronomy

Two observers stand at opposite poles and count stars visible from their respective positions. Each star is visible from exactly one pole, never both, which implies that the two observations partition the entire set of stars into two disjoint groups.
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CF 104678E - Football tournament

There are $n$ teams, each starting with a fixed strength value. Every pair of teams plays exactly one match, so the tournament is a complete round-robin.
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CF 104678D - Basic examination

We are given a string made only of opening and closing parentheses. The task is to decide whether this sequence could arise from some valid arithmetic expression after stripping away everything except parentheses.
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CF 104678C - Storybooks

We are given a collection of story lengths, where each story has a fixed number of pages. Alongside this, we are given several books, each with a page capacity.
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