Monthly Archives: January 2011

SGU 114 解题报告

http://acm.sgu.ru/problem.php?contest=0&problem=114

114. Telecasting station

time limit per test: 0.50 sec.
memory limit per test: 4096 KB

Every city in Berland is situated on Ox axis. The government of the country decided to build new telecasting station. After many experiments Berland scientists came to a conclusion that in any city citizens displeasure is equal to product of citizens amount in it by distance between city and TV-station. Find such point on Ox axis for station so that sum of displeasures of all cities is minimal.

Input

Input begins from line with integer positive number N (0<N<15000) – amount of cities in Berland. Following N pairs (X, P) describes cities (0<X, P<50000), where X is a coordinate of city and P is an amount of citizens. All numbers separated by whitespace(s).

Output

Write the best position for TV-station with accuracy 10-5.

Sample Input

4
1 3
2 1
5 2
6 2

Sample Output

3.00000

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SGU 144 解题报告

http://acm.sgu.ru/problem.php?contest=0&problem=144

144. Meeting

time limit per test: 0.50 sec.
memory limit per test: 4096 KB

Two of the three members of the winning team of one of the ACM regional contests are going to meet in order to train for the upcoming World Finals. They decided that they will meet sometime between X o'clock and Y o'clock. Because they never get anywhere on time (they were late even on the day of the regional contest), they did not set an exact time when they will meet. However, they decided that the one who gets first at the meeting point will not wait more than Z minutes for the other one (they calculated that, if the other one will not come within Z minutes from the arrival of the first of them, then it is very probable that he will not show up at all).
Knowing that, in the end, both of them will show up at some time between X o'clock and Y o'clock (not necessarily after an integer number of minutes), compute which is the probability that they will actually meet.

Input

The input will contain 2 integer numbers X and Y (0<=X<Y<=24) and one real number Z ( 0 < Z <= 60*(Y-X) ).

Output

You should output the required probability with 7 decimal digits (rounded according to the 8th decimal digit).

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.Net程序员:最简单方式掌握Linux本质(转载)

"If you can't explain it simply, you don't understand it well enough" Albert Einstein

有很多关于Linux的书籍,博客.大多数都会比较"粗暴"的将一大堆的命令塞给读者,从而使很多人望而却步.未入其门就路过了.

所以我设想用一种更为平滑的学习方式, 就是在学习命令时,先用纯语言来介绍Linux背景和动机. 就如同所有的的网络游戏都要先介绍游戏的历史观,然后再介绍游戏的操作.

大多数初学者在刚刚接触Linux都会有非常陌生的感觉.往往会有一些疑惑和问题.而我们就沿着这些问题,从远及近,从宏观到微观来理解Linux的简洁和美丽.

问题1: Winows有注册表,为什么Linux没有注册表

注册表是Windows核心组件,对整个系统进行配置.Linux是以整个文件系统作为"注册表",Windows注册表的树形结构,可以粗略的对应Linux文件系统的树形结构.

Linux的配置文件就相当于注册表的键,或者说Linux采用是的分布式的注册表.

那么Linux为什么要这样设计呢?因为Linux是所谓的网络操作系统,所以单台电脑不是Linux的界限,如果是多台电脑组成的系统,那么分布式的管理就有着巨大的优势.

例如:一个包含配置文件的磁盘的损害不会让整个系统瘫痪,而可能只是让部分功能失效.

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