http://codeforces.com/contest/30/problem/C 题意：给出n个target在一个二维平面上。给出每个target的坐标，出现的时间，以及击中的概率。target出现之后就会瞬间消失，枪移动的单位速度为1，射击不需要时间。问能击中的target的最大期望是多少。
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**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 …
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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 …
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