[原创]【待补】华中农业大学第五届程序设计大赛 B Choosy in Food [高斯消元]【数学】

2017-05-26 21:08:14 Tabris_ 阅读数：338

博客爬取于2020-06-14 22:40:37
以下为正文

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https://blog.csdn.net/qq_33184171/article/details/72773595

题目链接:http://acm.hzau.edu.cn/problem.php?id=1200
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1200: Choosy in Food
Time Limit: 1 Sec Memory Limit: 1280 MB
Submit: 48 Solved: 12
[Submit][Status][Web Board]
Description
Xiao Ming find n trees (labeled 0…n-1) which join a circle in a magical land. Each tree
is covered with ripe berries. Xiao Ming wants to find the tree whose berries are most delicious. He starts from the tree X, walks clockwise to find the target. Each time the probability of him walking k trees is Pk% . P1+P2+…+Pk = 100

Now we know the target of Xiao Ming is the tree Y. Require to know expectation of the number of the trees which Xiao Ming walk through

Input
The first parameter is T, indicates the case number.

In each case, there are four integers at the first line, N, M, X , Y (Tree labels from 0 to N-1, N < 100, M < N).

Output
The expectation of the number of trees Xiao Ming walk through. It will be reserved two decimal places. If Xiao Ming will never arrive the tree, output -1.

Sample Input
2
4 2 0 1
50 50
4 1 0 2
100
Sample Output
4.20
2.00

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题目大意：
就是有一些树（真的树，能结果子那种），围城一圈，编号0~n-1。一个人从X开始顺时针出发，可以走1~M步，每步的概率是 $P_i$ ,问你走到Y的期望步数是多少.

解题思路:

这种套路很明显的高斯消元啊.,但是我不会高斯消元啊.....

占坑待补…