问题 2353 --想见面不容易

2353: 想见面不容易

时间限制: 1 Sec  内存限制: 32 MB
提交: 98  解决: 33
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题目描述

之前的中文题意与测试数据有歧义,现把题目内容改为英文原题。


Xiaoming lives in a village but his girl friend lives in another village. He decided to follow the straight path between his house (A) and girl friend's house (B), but there are several rivers he needs to cross. Assume B is to the right of A, and all the rivers lie between them. 

 
Fortunately, there is one "automatic" boat moving smoothly in each river. When he arrives the left bank of a river, just wait for the boat, then go with it. He is so slim that carrying him does not change the speed of any boat. 
 
Days and days after, he came up with the following question: assume each boat is independently placed at random at time 0, what is the expected time to reach B from A? His walking speed is always 1. 
 
To be more precise, for a river of length L, the distance of the boat (which could be regarded as a mathematical point) to the left bank at time 0 is uniformly chosen from interval [0, L], and the boat is equally like to be moving left or right, if it’s not precisely at the river bank.

输入

There will be at most 10 test cases. Each case begins with two integers n and D, where n (0<=n<=10) is the number of rivers between A and B, D (1<=D<=1000) is the distance from A to B. Each of the following n lines describes a river with 3 integers: p, L and v (0<=p<D, 0<L<=D, 1<=v<=100). p is the distance from A to the left bank of this river, L is the length of this river, v is the speed of the boat on this river. It is guaranteed that rivers lie between A and B, and they don’t overlap. 
The last test case is followed by n=D=0, which should not be processed.

输出

For each test case, print the case number and the expected time, rounded to 3 digits after the decimal point. 
Print a blank line after the output of each test case.

样例输入

1 1
0 1 2
0 1
0 0

样例输出

Case 1: 1.000

Case 2: 1.000

来源

 

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