时间限制：1 秒

内存限制：128 兆

特殊判题：否

提交：1431

解决：641

题目描述：

FatMouse prepared M pounds of cat food, ready to trade with the cats guarding the warehouse containing his favorite food, JavaBean.
The warehouse has N rooms. The i-th room contains J[i] pounds of JavaBeans and requires F[i] pounds of cat food. FatMouse does not have to trade for all the JavaBeans in the room, instead, he may get J[i]* a% pounds of JavaBeans if he pays F[i]* a% pounds of cat food. Here a is a real number. Now he is assigning this homework to you: tell him the maximum amount of JavaBeans he can obtain.

输入：

The input consists of multiple test cases. Each test case begins with a line containing two non-negative integers M and N. Then N lines follow, each contains two non-negative integers J[i] and F[i] respectively. The last test case is followed by two -1's. All integers are not greater than 1000.

输出：

For each test case, print in a single line a real number accurate up to 3 decimal places, which is the maximum amount of JavaBeans that FatMouse can obtain.

样例输入：

5 3
7 2
4 3
5 2
20 3
25 18
24 15
15 10
-1 -1

样例输出：

13.333
31.500

 #include <iostream>

 #include <algorithm>

 #include <iomanip>

 using namespace std;

 struct goods

 {

    int J,F;

    double xinjia;

 }buf[];

 bool cmp(goods a,goods b)

 {

     return  a.xinjia<b.xinjia;

 }

 int main()

 {

   int m,n,j,f;

   while(cin>>m)

   {

      cin>>n;

      if(m==-&&n==-) break;

      int i;

      for(i=;i<n;i++)

      {

        cin>>j>>f;

        buf[i].J=j;

        buf[i].F=f;

        buf[i].xinjia=(double)f/j;

      }

      sort(buf,buf+n,cmp);

      double sum=0.0;

      for(i=;i<n;i++)

      {

         if(buf[i].F<m)

         {

            sum=sum+buf[i].J;

            m=m-buf[i].F;

         }

         else

         {

            sum=sum+buf[i].J*(double)m/buf[i].F;

            break;

         }

      }

      cout<<fixed<<setprecision()<<sum<<endl;

   }

   return ;

 }

 /**************************************************************

     Problem: 1433

     User: 2009declan

     Language: C++

     Result: Accepted

     Time:10 ms

     Memory:1536 kb

 ****************************************************************/