10
7
2015
0

CF289 Div2 F. Progress Monitoring

F. Progress Monitoring
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Programming teacher Dmitry Olegovich is going to propose the following task for one of his tests for students:

You are given a tree T with n vertices, specified by its adjacency matrix a[1... n, 1... n]. What is the output of the following pseudocode?

Category: codeforces | Tags:
9
17
2015
0

C. Jzzhu and Apples

C. Jzzhu and Apples
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Jzzhu has picked n apples from his big apple tree. All the apples are numbered from 1 to n. Now he wants to sell them to an apple store.

Jzzhu will pack his apples into groups and then sell them. Each group must contain two apples, and the greatest common divisor of numbers of the apples in each group must be greater than 1. Of course, each apple can be part of at most one group.

Jzzhu wonders how to get the maximum possible number of groups. Can you help him?

Category: codeforces | Tags:
9
17
2015
0

CF257Div1 A. Jzzhu and Chocolate

A. Jzzhu and Chocolate
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

Jzzhu has a big rectangular chocolate bar that consists of n × m unit squares. He wants to cut this bar exactly k times. Each cut must meet the following requirements:

  • each cut should be straight (horizontal or vertical);
  • each cut should go along edges of unit squares (it is prohibited to divide any unit chocolate square with cut);
  • each cut should go inside the whole chocolate bar, and all cuts must be distinct.

The picture below shows a possible way to cut a 5 × 6 chocolate for 5 times.

Imagine Jzzhu have made k cuts and the big chocolate is splitted into several pieces. Consider the smallest (by area) piece of the chocolate, Jzzhu wants this piece to be as large as possible. What is the maximum possible area of smallest piece he can get with exactlyk cuts? The area of a chocolate piece is the number of unit squares in it.

Category: codeforces | Tags:
9
12
2015
0

C. Lucky Subsequence

C. Lucky Subsequence
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

Petya loves lucky numbers very much. Everybody knows that lucky numbers are positive integers whose decimal record contains only the lucky digits 4 and 7. For example, numbers 477444 are lucky and 517467 are not.

Petya has sequence a consisting of n integers.

The subsequence of the sequence a is such subsequence that can be obtained from a by removing zero or more of its elements.

Two sequences are considered different if index sets of numbers included in them are different. That is, the values ​of the elements ​do not matter in the comparison of subsequences. In particular, any sequence of length n has exactly 2n different subsequences (including an empty subsequence).

A subsequence is considered lucky if it has a length exactly k and does not contain two identical lucky numbers (unlucky numbers can be repeated any number of times).

Help Petya find the number of different lucky subsequences of the sequence a. As Petya's parents don't let him play with large numbers, you should print the result modulo prime number 1000000007 (109 + 7).

Category: codeforces | Tags:

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