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

 1 #include <iostream> 2 #include <algorithm> 3 #include <iomanip> 4 using namespace std; 5   6 struct goods 7 { 8    int J,F; 9    double xinjia;10 }buf[1000];11  12  13 bool cmp(goods a,goods b)14 {15  16     return  a.xinjia<b.xinjia;17 }18  19  20 int main()21 {22   int m,n,j,f;23   while(cin>>m)24   {25      cin>>n;26      if(m==-1&&n==-1) break;27      int i;28      for(i=0;i<n;i++)29      {30        cin>>j>>f;31        buf[i].J=j;32        buf[i].F=f;33        buf[i].xinjia=(double)f/j;34      }35      sort(buf,buf+n,cmp);36       37      double sum=0.0;38      for(i=0;i<n;i++)39      {40         if(buf[i].F<m)41         {42            sum=sum+buf[i].J;43            m=m-buf[i].F;44         }45         else46         {47            sum=sum+buf[i].J*(double)m/buf[i].F;48            break;49         }50      }51  52      cout<<fixed<<setprecision(3)<<sum<<endl;53       54      55   }56   return 0;57 }58  59 /**************************************************************60     Problem: 143361     User: 2009declan62     Language: C++63     Result: Accepted64     Time:10 ms65     Memory:1536 kb66 ****************************************************************/