1.3 mixing milk 简单贪心算法

最新推荐文章于 2025-01-21 19:21:38 发布

原创最新推荐文章于 2025-01-21 19:21:38 发布 · 810 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#算法 #output #each #integer #file #struct

USACO 专栏收录该内容

26 篇文章

订阅专栏

本文介绍了一个简单的贪心算法，用于帮助 MerryMilkMakers 公司以最低成本从多个农民那里购买所需数量的牛奶。算法首先按单价排序农民提供的牛奶价格，然后依次从最低价开始购买，直至满足需求。

Mixing Milk

Since milk packaging is such a low margin business, it is important to keep the price of the raw product (milk) as low as possible. Help Merry Milk Makers get the milk they need in the cheapest possible manner.

The Merry Milk Makers company has several farmers from which they may buy milk, and each one has a (potentially) different price at which they sell to the milk packing plant. Moreover, as a cow can only produce so much milk a day, the farmers only have so much milk to sell per day. Each day, Merry Milk Makers can purchase an integral amount of milk from each farmer, less than or equal to the farmer's limit.

Given the Merry Milk Makers' daily requirement of milk, along with the cost per gallon and amount of available milk for each farmer, calculate the minimum amount of money that it takes to fulfill the Merry Milk Makers' requirements.

Note: The total milk produced per day by the farmers will be sufficient to meet the demands of the Merry Milk Makers.

PROGRAM NAME: milk

INPUT FORMAT

Line 1:	Two integers, N and M. The first value, N, (0 <= N <= 2,000,000) is the amount of milk that Merry Milk Makers' want per day. The second, M, (0 <= M <= 5,000) is the number of farmers that they may buy from.
Lines 2 through M+1:	The next M lines each contain two integers, P_i and A_i . P_i (0 <= P_i <= 1,000) is price in cents that farmer i charges. A_i (0 <= Ai <= 2,000,000) is the amount of milk that farmer i can sell to Merry Milk Makers per day.

SAMPLE INPUT (file milk.in)

OUTPUT FORMAT

A single line with a single integer that is the minimum price that Merry Milk Makers can get their milk at for one day.

SAMPLE OUTPUT (file milk.out)

630



/*
ID: xdzhbin1
LANG: C++
TASK:milk
*/

#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;
//简单贪心算法

//每个农户的数据
typedef struct Node
{
	int amount;//牛奶总量
	int charge;//单价
}Node ;

//自定义比较函数，依据是单价
bool cmp(Node n1, Node n2)
{
	return n1.charge < n2.charge;
}

int main()
{
	ifstream in("milk.in",ios::in);
	ofstream out("milk.out",ios::out);

	int nMilk,nFormer;
	in>>nMilk>>nFormer;//读入需求总量和农户个数

	vector<Node> formers(nFormer);
	int i = 0;

	while(i<nFormer)
	{
		in>>formers[i].charge>>formers[i].amount;//读入每个农户的信息
		i++;
	}

	sort(formers.begin(),formers.end(),cmp);//排序
	int moneys = 0;
	i = 0;
	while(nMilk>0)
	{
		if(formers[i].amount<nMilk)	//从最便宜的买起
		{
			nMilk -= formers[i].amount;
			moneys += formers[i].amount * formers[i].charge;
		}
		else
		{
			moneys += nMilk * formers[i].charge;
			nMilk  -= nMilk;
		}
		i++;
	}
	out<<moneys<<endl;
	return 0;
}