杭电2187

#include <iostream>#include <cstdio>#include <algorithm>using namespace std;struct node{int price,weight;}stu[1100];bool cmp(node x,node y){return x.price<y.price;}int main(){int C,n,m,i,num;double sum;scanf("%d",&C);while(C--){sum=0;scanf("%d%d",&n,&m);for(i=1;i<=m;i++){scanf("%d%d",&stu[i].price,&stu[i].weight);}sort(stu+1,stu+m+1,cmp);for(i=1;i<=m;i++){num=stu[i].price*stu[i].weight;if(n>=num){n-=num;sum+=stu[i].weight;}else {sum+=1.0*n/num*stu[i].weight;break;}}printf("%.2f\n",sum);}return 0;}