主要的难点是两个变量，求最大值，按照数学的思想，除非这两个有某种联系，然后利用单调性求解，否则只有一条出路，定其中一个变量。
当min(B) 或者sum(P) 确定后，剩下的工作就是就最小值。显然这里定min(B)较为合理，毕竟sum(P)还需要求和。

```
#include<iostream>
#include<string>
#include <iomanip>
#include <fstream>  
using namespace std;

struct BPData
{
	int bandWidth;
	int price;
};

int test_size;
int product_size;
int product_case[100] = {};
BPData detail[100][100] = {};
int max_search_bandwidth = 65535;

//求B/P值
double getBP(int minBandWidth)
{
	//下次使用的minBandwidth，由于要更新minBandwidth，所以感觉排序没太大必要
	int nextBandWidth = 0;
	int sum_price = 0;
	for (int i = 0; i < product_size; i++)
	{
		int temp_price = 65535;
		for (int j = 0; j < product_case[i]; j++)
		{
			if (detail[i][j].bandWidth >= minBandWidth)
			{
				if (temp_price > detail[i][j].price)
				{
					temp_price = detail[i][j].price;
				}
			}
			else if (nextBandWidth < detail[i][j].bandWidth) // 寻找下一个banwidth
				{
					nextBandWidth = detail[i][j].bandWidth;
				}
		}
		sum_price += temp_price;
	}
	//计算当前值
	double temp_result = ((double)minBandWidth) / sum_price;
	if (nextBandWidth)
	{
		double next_result = getBP(nextBandWidth);
		return next_result > temp_result ? next_result : temp_result;
	}
	return temp_result;
}


int main()
{
//	ifstream in("d:\\document\\test.txt");
	cin >> test_size;
	int sum_test = 0;
		while (sum_test < test_size)
		{
			max_search_bandwidth = 65535;
			sum_test++;
			cin >> product_size;
			for (int i = 0; i < product_size; i++)
			{
				cin >> product_case[i];
				int line_max = 0;
				for (int j = 0; j < product_case[i]; j++)
				{
					cin >> detail[i][j].bandWidth >> detail[i][j].price;
					if (line_max < detail[i][j].bandWidth)
					{
						line_max = detail[i][j].bandWidth;
					}
				}
				if (max_search_bandwidth > line_max)
				{
					max_search_bandwidth = line_max;
				}
			}
			double bp = getBP(max_search_bandwidth);
			cout.setf(ios::fixed);
			cout << fixed << setprecision(3) << bp << endl;
		}
	system("pause");
	return 0;
}
```