hdu 1.3.1 FatMouse' Trade

贪心的运用，主要看其比值，取最大值实现贪心...

 #include<cstdio>
 #include<algorithm>
 #include<vector>
 using namespace std;

 struct room
 {
     int j;
     int f;
     bool operator < (const room t)const
     {
         return (float)j/f >(float)t.j/t.f;
     }
 };

 int main()
 {
     //freopen("input.txt","r",stdin);
     int m,n,i;
     double ans;
     while(scanf("%d%d",&m,&n) && (m+) &&(n+))
     {
         vector<room> v;
         room r;
         ans = ;
         for(i = ; i < n; i++)
         {
             scanf("%d%d",&r.j,&r.f);
             v.push_back(r);
         }
         sort(v.begin(),v.end());

         i = ;
         while(m >  && i < v.size())
         {
             if(v[i].f <= m)
             {
                 m -= v[i].f;
                 ans += v[i].j;
             }
             else
             {
                 ans += (double)(v[i].j* m)/v[i].f ;
                 m = ;//½áÊø
             }
             i++;
         }
         printf("%.3lf\n",ans);
     }

     return ;
 }