zoukankan      html  css  js  c++  java
  • POJ

    Discription
    Ivan is fond of collecting. Unlike other people who collect post stamps, coins or other material stuff, he collects software bugs. When Ivan gets a new program, he classifies all possible bugs into n categories. Each day he discovers exactly one bug in the program and adds information about it and its category into a spreadsheet. When he finds bugs in all bug categories, he calls the program disgusting, publishes this spreadsheet on his home page, and forgets completely about the program. 
    Two companies, Macrosoft and Microhard are in tight competition. Microhard wants to decrease sales of one Macrosoft program. They hire Ivan to prove that the program in question is disgusting. However, Ivan has a complicated problem. This new program has s subcomponents, and finding bugs of all types in each subcomponent would take too long before the target could be reached. So Ivan and Microhard agreed to use a simpler criteria --- Ivan should find at least one bug in each subsystem and at least one bug of each category. 
    Macrosoft knows about these plans and it wants to estimate the time that is required for Ivan to call its program disgusting. It's important because the company releases a new version soon, so it can correct its plans and release it quicker. Nobody would be interested in Ivan's opinion about the reliability of the obsolete version. 
    A bug found in the program can be of any category with equal probability. Similarly, the bug can be found in any given subsystem with equal probability. Any particular bug cannot belong to two different categories or happen simultaneously in two different subsystems. The number of bugs in the program is almost infinite, so the probability of finding a new bug of some category in some subsystem does not reduce after finding any number of bugs of that category in that subsystem. 
    Find an average time (in days of Ivan's work) required to name the program disgusting.

    Input

    Input file contains two integer numbers, n and s (0 < n, s <= 1 000).

    Output

    Output the expectation of the Ivan's working days needed to call the program disgusting, accurate to 4 digits after the decimal point.

    Sample Input

    1 2

    Sample Output

    3.0000


    暴力期望dp即可。

    /*
        f[a][b] -> f[a][b] ( a/n * b/m)
        f[a][b] -> f[a+1][b] ( (n-a)/n * b/m)
        f[a][b] -> f[a][b+1] ( a/n * (m-b)/m)
        f[a][b] -> f[a+1][b+1] ( (n-a)/n * (m-b)/m)
        
        
    */
    #include<cstdio>
    #define ll long long
    using namespace std;
    #define D long double
    const int maxn=1005;
    
    D f[maxn][maxn],A,B;
    int n,m;
    
    inline void solve(){
    	for(int i=n;i>=0;i--)
    	    for(int j=(i==n?m-1:m);j>=0;j--){
    	    	f[i][j]=f[i+1][j]*(n-i)*j+f[i][j+1]*i*(m-j)+f[i+1][j+1]*(n-i)*(m-j)+n*m;
    	    	f[i][j]/=(D)(n*(ll)m-i*j);
    		}
    }
    
    int main(){
    //	freopen("data.in","r",stdin);
    //	freopen("data.out","w",stdout);
    	
    	scanf("%d%d",&n,&m);
    	solve();
    	printf("%.4lf
    ",f[0][0]);
    	return 0;
    }
    

      

    
    
  • 相关阅读:
    mode
    Jmeter获取不到cookie(备注:前面和后面的几个步骤都可以获取到cookie)
    [BAT]批处理脚本双击可运行,但在定时计划任务中无法执行(当前工作路径不对导致的)
    匹配数字、字母和?%&=-_这几个符号的正则表达式
    在jmeter的beanshell中用java获取系统当前时间
    Jmeter中正则表达式不区分大小写进行匹配
    通过BeanShell获取UUID并将参数传递给Jmeter
    JAVA Get UUID
    Jmeter报文体包含过大附件导致请求报文发送失败的解决办法
    [BAT]操作系统定时任务调用批处理忽略error继续运行的方法
  • 原文地址:https://www.cnblogs.com/JYYHH/p/9163487.html
Copyright © 2011-2022 走看看