http://codeforces.com/contest/621/problem/C
C. Wet Shark and Flowers
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
There are n sharks who grow flowers for Wet Shark. They are all sitting around the table, such that sharks i and i + 1 are neighbours for all i from 1 to n - 1. Sharks n and 1 are neighbours too.
Each shark will grow some number of flowers s__i. For i-th shark value s__i is random integer equiprobably chosen in range from _l__i_to r__i. Wet Shark has it’s favourite prime number p, and he really likes it! If for any pair of neighbouring sharks i and j the product s__i·s__j is divisible by p, then Wet Shark becomes happy and gives 1000 dollars to each of these sharks.
Desiderium # **Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 65536/65536 K (Java/Others) Total Submission(s): 427 Accepted Submission(s): 167 **
Problem Description
There is a set of intervals, the size of this set is n.
If we select a subset of this set with equal probability, how many the expected length of intervals’ union of this subset is?
We assume that the length of empty set’s union is 0, and we want the answer multiply 2n modulo 109+7.
B. Andrey and Problem
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Andrey needs one more problem to conduct a programming contest. He has n friends who are always willing to help. He can ask some of them to come up with a contest problem. Andrey knows one value for each of his fiends – the probability that this friend will come up with a problem if Andrey asks him.