Random signals
Time limit12sMemory limit256 MB
Compute the expected plane integral of the strongest covering signal when each of up to 20 stations draws an independent uniform power that activates its disks.
- Level
Hard9 of 10
- Topics
- Geometry, Probability, Combinatorics
- Solved
- No attempts yet
Problem
There are signal stations on the plane, numbered 1 to . Station is at and broadcasts into a disk centered at that point. The radius and the strength of a broadcast depend on how much power the station receives.
Station can send different signals, named through . Signal has radius and strength , and station always sends it once the power that reaches the station is at least . So when station receives power , every signal with goes out, and each of those signals covers every point of the closed disk with center and radius .
The strength delivered to a point is the largest strength among the signals that cover it. If no signal covers the point, the strength there is . The government measures how far the signals spread with the value below.
Each day the government picks the power for station among the integers in . Every integer is equally likely, and the stations are chosen independently of each other. Compute the expected value of .
Input
The first line contains the number of stations ().
The descriptions of the stations follow in order, starting with station 1. The first line of each description contains five integers , (), (), and (), separated by spaces. Each of the next lines contains three integers , and (), separated by spaces.
Output
Print the expected value of on one line, rounded to six digits after the decimal point. Print exactly six digits after the decimal point.
Every input satisfies two guarantees: the expected value is smaller than , and it is at least away from the boundary where rounding to six decimal digits switches between rounding up and rounding down.