关于【贪心算法】

FatMouse

题目描述：

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.

输入：

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.

输出：

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.

样例输入：

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

样例输出：

13.333
31.500

Code:

#include <cstdio>
#include <algorithm>

using namespace std;

struct goods{
    double weight;        //该物品总重
    double totalValue;    //该物品总价值
    double price;         //该物品性价比
};

bool cmp(goods a,goods b){
    return a.price>=b.price;
}

int main()
{
    double n;   //一共多少钱
    const int arrSize=1010;
    int m;      //有几样物品
    goods arr[arrSize];
    while(scanf("%lf%d",&n,&m)!=EOF){
        if(n==-1&&m==-1)
            break;
        for(int cnt=0;cnt<m;++cnt){
            scanf("%lf%lf",&arr[cnt].weight,&arr[cnt].totalValue);
            arr[cnt].price=arr[cnt].weight/arr[cnt].totalValue;
        }
        sort(arr,arr+m,cmp);
        double ans=0;
        int index=0;
        while(n>0&&index<m){
            if(n>arr[index].totalValue){   //若能买下全部该商品
                ans+=arr[index].weight;
                n-=arr[index].totalValue;
            }else{
                ans+=n/arr[index].totalValue*arr[index].weight;
                n=0;
            }
            ++index;
        }
        printf("%.3lf\n",ans);
    }
    return 0;
}

/**************************************************************
    Problem: 1433
    User: lcyvino
    Language: C++
    Result: Accepted
    Time:10 ms
    Memory:1020 kb
****************************************************************/