水题必须的，果断用struct排序再计算，第一次循环条件搞错WA了一次。。。

[cpp]
#include
#include
#define MAXN 10000
using namespace std;

struct Room{
int j, f;
double value;
};
Room r[MAXN];

bool cmp(Room a, Room b)
{
return a.value > b.value;
}

int main()
{
int m, n;
while (scanf("%d%d", &m, &n) && m != -1 && n != -1)
{
for (int i = 0; i < n; i++)
{
scanf("%d%d", &r[i].j, &r[i].f);
r[i].value = (double) r[i].j / (double) r[i].f;
}
sort(r, r + n, cmp); //排序
double sum = 0;
for (int i = 0; i < n; i++)
if (m >= r[i].f)
sum += r[i].j, m -= r[i].f; //循环加进能全部拿到的东西
else
{
sum += (double) m * r[i].value; //最后一个房间只能拿一部分
break; //拿完跳出循环
}
printf("%.3f\n", sum);
}
return 0;
}

#include
#include
#define MAXN 10000
using namespace std;

struct Room{
int j, f;
double value;
};
Room r[MAXN];

bool cmp(Room a, Room b)
{
return a.value > b.value;
}

int main()
{
int m, n;
while (scanf("%d%d", &m, &n) && m != -1 && n != -1)
{
for (int i = 0; i < n; i++)
{
scanf("%d%d", &r[i].j, &r[i].f);
r[i].value = (double) r[i].j / (double) r[i].f;
}
sort(r, r + n, cmp);//排序
double sum = 0;
for (int i = 0; i < n; i++)
if (m >= r[i].f)
sum += r[i].j, m -= r[i].f;//循环加进能全部拿到的东西
else
{
sum += (double) m * r[i].value;//最后一个房间只能拿一部分
break;//拿完跳出循环
}
printf("%.3f\n", sum);
}
return 0;
}
慢慢地追随E.star大神的脚步了。。。