HD1009 经典贪心

#include <iostream>
#include <algorithm>
#include <fstream>
#include <iomanip>
using namespace std;
#define MAX 1000
struct room
{
	int f,j;
	double rate;
	bool operator<(room r)
	{
		return rate>r.rate;
	}
};
room rooms[MAX];
int main()
{
	int m=-1,n=-1;
	//ifstream cin("input.txt");
	room r;
	int index;
	double sum;
	while (cin>>m>>n && m!=-1 && n!=-1)
	{
		index=0;
		sum=0.0;
		for(int i=0;i<n;i++)
		{
			cin>>r.j>>r.f;
			r.rate=r.j*1.0/r.f;
			rooms[i]=r;
		}
		sort(rooms,rooms+n);
		for (int i=0;i<n;i++)
		{
			if(rooms[i].f<m)
			{
				sum+=rooms[i].j;
				m=m-rooms[i].f;
			}
			else
			{
				sum+=m*rooms[i].rate;
				m=0;
			}
		}
		cout<<setprecision(3)<<setiosflags(ios::fixed | ios::showpoint)<<sum<<endl;
		m=n=-1;
	}
	return 0;
}