HDU 1009 FatMouse' Trade（贪心）

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

#include<stdio.h>
#include<algorithm>
using namespace std;
int m,n;
struct x{
    int j,c;
    double q;
}a[1010];
bool cmp(x a,x b){//贪心，按照最少的猫粮换最多的老鼠吃的排序 
    return a.q>b.q;
}

int main(){
    while(scanf("%d%d",&m,&n)!=EOF){
        if(m==-1&&n==-1){
            break;
        }
        for(int i=1;i<=n;i++){
            scanf("%d%d",&a[i].j,&a[i].c);
            a[i].q=a[i].j/(1.0*a[i].c);//求出每组的转化率 
        }                 //乘以0.1，转化为浮点型 
        sort(a+1,a+1+n,cmp);
        double sum=0;
        for(int i=1;i<=n;i++){
            if(m>=a[i].c){//如果老鼠手里有的猫粮比要求的多，把所有的老鼠吃的都换来 
                sum+=a[i].j;//加上换来的鼠粮 
                m-=a[i].c;//手里剩下的猫粮 
            }
            else{
                sum+=a[i].q*m;//不足，就按比例换 
                m-=m;
            }
            if(m==0){
                break;
            } 
        }
        printf("%.3f\n",sum);
    }
} 

（寒いですね）