hdu 1009 FatMouse' Trade(胖老鼠的交易)

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
struct trate
{
double food ,javabin;
double t;
}w[1005];
bool cmp(trate a, trate b)
{
if(a.t>b.t)
return true;
return false;
}
int main()
{
int m,n;
double sum;
while(scanf("%d%d",&m,&n))
{
if(m==-1&&n==-1)
break;
for(int i=0;i<n;i++)
{
scanf("%lf%lf",&w[i].food,&w[i].javabin);
w[i].t=w[i].food*1.0/w[i].javabin;
}
sort(w,w+n,cmp);
sum=0;
for(int i=0;i<n;i++)
{
if(m>w[i].javabin)
{
sum+=w[i].food;
m-=w[i].javabin;
}
else
{
sum+=w[i].t*m;
break;
}
}
printf("%.3lf\n",sum);
}
return 0;
}