1070 Mooncake（贪心算法）

1070 Mooncake （25 分）

Mooncake is a Chinese bakery product traditionally eaten during the Mid-Autumn Festival. Many types of fillings and crusts can be found in traditional mooncakes according to the region’s culture. Now given the inventory amounts and the prices of all kinds of the mooncakes, together with the maximum total demand of the market, you are supposed to tell the maximum profit that can be made.

Note: partial inventory storage can be taken. The sample shows the following situation: given three kinds of mooncakes with inventory amounts being 180, 150, and 100 thousand tons, and the prices being 7.5, 7.2, and 4.5 billion yuans. If the market demand can be at most 200 thousand tons, the best we can do is to sell 150 thousand tons of the second kind of mooncake, and 50 thousand tons of the third kind. Hence the total profit is 7.2 + 4.5/2 = 9.45 (billion yuans).

Input Specification:

Each input file contains one test case. For each case, the first line contains 2 positive integers N (≤1000), the number of different kinds of mooncakes, and D (≤500 thousand tons), the maximum total demand of the market. Then the second line gives the positive inventory amounts (in thousand tons), and the third line gives the positive prices (in billion yuans) of N kinds of mooncakes. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the maximum profit (in billion yuans) in one line, accurate up to 2 decimal places.

Sample Input:

3 200
180 150 100
7.5 7.2 4.5

Sample Output:

9.45

分析

本题考查贪心算法，难度不大，但是关于市场最大需求量D和货物供应量amount的数据类型选型涉及到测试点2（从0开始）是否能通过。题面表述D和N时指出两个 正整数，因此D的类型选为int，对于amount的类型，题面没有明说，这个需要我们仔细观察和揣摩 ( 隐藏的失分点)，依据生活经验，amount的单位是thousand ton，amount存在小数的可能，所以讲amount的类型定为double.

#include<iostream> 
#include <vector>
#include <algorithm>
using namespace std;
struct node{
	double amount,prices;
};
bool cmp(node a,node b){
	return a.prices/a.amount>b.prices/b.amount;
}
int main(){
	int n,d;
	cin>>n>>d;
	vector<node> v(n);
	for(int i=0;i<n;i++) cin>>v[i].amount;
	for(int i=0;i<n;i++) cin>>v[i].prices;
	sort(v.begin(),v.end(),cmp);
	double profit=0.0;
	int k=0;
	while(d>0 && k<n){
		if(d>v[k].amount){
			profit+=v[k].prices;
			d-=v[k].amount;
			k++;
		}else{
			profit+=v[k].prices*d/v[k].amount;
			d=0;
		}
	}
	printf("%.2lf\n",profit);
	return 0;
}