FatMouse' Trade

Problem Description

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.

 

Input

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.

 

Output

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.

 

Sample Input

5 3

7 2

4 3

5 2

20 3

25 18

24 15

15 10

-1 -1

 

Sample Output

13.333

31.500

 

#include <stdio.h> 
#define N 1001

int main(){
    int m;
    int n;
    int i;
    int j;
    int J[N];
    int F[N];
    double unit[N];
    double temp;
    double get;

    while(1){
        scanf("%d%d",&m,&n);

        if(m==-1 && n==-1)
            break;

        get=0;
        for(i=0;i<n;i++){
            scanf("%d%d",&J[i],&F[i]);
            unit[i]=(double)J[i]/F[i];
        }

        for(i=0;i<n-1;i++){
            for(j=i+1;j<n;j++){
                if(unit[i]<unit[j]){
                    temp=unit[i];
                    unit[i]=unit[j];
                    unit[j]=temp;

                    temp=J[i];
                    J[i]=J[j];
                    J[j]=temp;

                    temp=F[i];
                    F[i]=F[j];
                    F[j]=temp;
                }
            }
        }

        
        for(i=0;i<n;i++){
            if(m>=F[i]){
                m=m-F[i];
                get+=J[i];   //这里J[i]改成unit[i]*F[i]会丢失精度导致出错

                if(m==0)
                    break;
            }

            else{
                get+=unit[i]*m;
                    
                break;
            }
        }
        printf("%.3lf\n",get);
    }    
    return 0;
}