HDOJ 1009 FatMouse' TradeD

Problem Description

FatMouse prepared M pounds of cat food, ready to trade with the cats guarding the warehouse containing his favorite food, JavaBean.

The warehouse has N rooms. The i-th room contains J[i] pounds of JavaBeans and requires F[i] pounds of cat food. FatMouse does not have to trade for all the JavaBeans in the room, instead, he may get J[i]* a% pounds of JavaBeans if he pays F[i]* a% pounds of
cat food. Here a is a real number. Now he is assigning this homework to you: tell him the maximum amount of JavaBeans he can obtain.

Input

The input consists of multiple test cases. Each test case begins with a line containing two non-negative integers M and N. Then N lines follow, each contains two non-negative integers J[i] and F[i] respectively. The last test case is followed by two -1's. All
integers are not greater than 1000.

Output

For each test case, print in a single line a real number accurate up to 3 decimal places, which is the maximum amount of JavaBeans that FatMouse can obtain.

Sample Input

5 3
7 2
4 3
5 2
20 3
25 18
24 15
15 10
-1 -1

Sample Output

13.333
31.500//
//  main.cpp
//  FatMouse' Trade
//
//  Created by 张嘉韬 on 16/3/8.
//  Copyright © 2016年 张嘉韬. All rights reserved.
//

#include <iostream>
#include <cstring>
#include <algorithm>
const int maxn=1010;
using namespace std;
struct room
{
double j;
double f;
double a;
}rooms[maxn];
int cmp(const void *a,const void *b)
{
return (*(room *)a).a>(*(room *)b).a?-1:1;
}
int main(int argc, const char * argv[]) {
int m,n;
while(scanf("%d%d",&m,&n)==2)
{
double sum=0;
if(m==-1&&n==-1) break;
else
{
for(int i=0;i<n;i++)
{
cin>>rooms[i].j>>rooms[i].f;
rooms[i].a=rooms[i].j/rooms[i].f;
}
qsort(rooms,n,sizeof(rooms[0]),cmp);
//            for(int i=0;i<n;i++) cout<<rooms[i].a<<endl;
for(int i=0;i<n;i++)
{
if(m>=rooms[i].f)
{
sum+=rooms[i].j;
m=m-rooms[i].f;
}
else
{
sum+=rooms[i].a*m;
//cout<<"("<<sum<<")"<<endl;
break;
}
//cout<<"("<<sum<<")"<<endl;

}
//cout<<sum<<endl;
printf("%.3f",sum);
cout<<endl;
}
}
return 0;
}