hdu 1009 FatMouse' Trade

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 <iostream>
#include <vector>
#include <iomanip>
#include <algorithm>

using namespace std;

struct FoodTrade
{
	int catFood;
	int javaBean;
	double rate;
};

bool cmp(FoodTrade x, FoodTrade y)
{
	return x.rate > y.rate;
}

class FatMouseTrade
{
public:
	void initialize();
	void readCase(const int& m, int& n);
	void compute();
	void output();
private:
	int catFood;
	vector<FoodTrade> foodTrade;
	double amount;
};

void FatMouseTrade::initialize()
{
	catFood = 0;
	amount = 0;
	foodTrade.clear();
}

void FatMouseTrade::readCase(const int& m, int& n)
{
	catFood = m;
	while(n--)
	{
		FoodTrade food;
		cin >> food.javaBean >> food.catFood;
		food.rate = static_cast<double>(food.javaBean) / food.catFood;
		foodTrade.push_back(food);
	}
}

void FatMouseTrade::compute()
{
	sort(foodTrade.begin(), foodTrade.end(), cmp);
	for(int i = 0; i < foodTrade.size() && catFood != 0; ++i)
	{
		if(catFood < foodTrade[i].catFood)
		{
			amount += foodTrade[i].rate * catFood;
			catFood = 0;
		}
		else
		{
			catFood -= foodTrade[i].catFood;
			amount += foodTrade[i].javaBean;
		}
	}
}

void FatMouseTrade::output()
{
	cout << setprecision(3) << setiosflags(ios::showpoint) << setiosflags(ios::fixed) << amount << endl;
}

int main()
{
	FatMouseTrade fatMouseTrade;
	int m, n;
	while(cin >> m >> n && m != -1 && n != -1)
	{
		fatMouseTrade.initialize();
		fatMouseTrade.readCase(m, n);
		fatMouseTrade.compute();
		fatMouseTrade.output();
	}
	return 0;
}

贪心算法