HDOJ 1019

AC代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm> 
using namespace std;

#define Max 1005

struct Warehous
{
    int M_Food;
    int C_Food;
    double s_value;
}wh[Max];

int T_CF, n;

bool compare(Warehous a, Warehous b)
{
    return a.s_value > b.s_value;
}

int main(void)
{
    freopen("in.txt","r",stdin);
    while(scanf("%d%d", &T_CF, &n) &&( T_CF != -1 || n != -1))
    {
        for(int i = 1; i <= n; i++)
            scanf("%d%d", &wh[i].M_Food, &wh[i].C_Food);    //输入
            
         for(int i = 1; i <= n; i++)
             wh[i].s_value = (double)wh[i].M_Food / wh[i].C_Food;
             
        sort(wh + 1, wh + n + 1, compare);     //排序，降序 
        
        double t_value = 0;     //总收益
        
         for(int i = 1; i <= n; i++)
         {
             if(T_CF >= wh[i].C_Food)
             {
                 T_CF -= wh[i].C_Food;
                 t_value +=wh[i].M_Food;
            }
             else
             {
                 t_value += (double)T_CF * wh[i].s_value;
                 T_CF = 0;
                 break;
            }
             
         } 
         
         printf("%.3lf\n", t_value);
    }
    
    
    
    fclose(stdin);
    system("pause");
    return 0;
}