题解

#include <bits/stdc++.h>
using namespace std;
const int N = 100001;
struct stu{
	double w;
	double v; 
	double wv;
}a[N];
bool cmp(stu aa,stu bb)
{
	return aa.wv>bb.wv;
}

int main()
{
	int k;
	cin>>k;
	while(k--)
	{
		int n,m;
		cin>>m>>n;
		for(int i=1;i<=n;++i)
		{
			cin>>a[i].w>>a[i].v;
			a[i].wv = a[i].v / a[i].w; 
		} 
		sort(a+1,a+1+n,cmp);
		double sum = 0;
		for(int i=1;i<=n;++i)
		{
			if(m>=a[i].w) 
				sum+=a[i].v;
			 
			 else sum+=m*a[i].wv;
			 
			 m-=a[i].w;
			 if(m<=0) break; 
		}
		printf("%.2f\n",sum);
	}
 
	return 0;
}