这个问题大概是这样的：一个牛奶公司从农民那里收取牛奶，第一行是输入的是N、M，N是这个公司收取要收取的牛奶总量，M是农民的人数。
以下M行是这M个农民的数据，一行包括两个数据P、A，P代表的是单位数量的牛奶的价格，P是这个农民可以送的牛奶量！
编写一个程序用最少的钱数去购买N这些的牛奶！从这五个数据里挑选！
例：
输入：
100 5
5 20
9 40
3 10
8 80
6 30
输出：
630

[此贴子已经被作者于2006-11-15 12:26:46编辑过]

这是原题！有一些取值范围的要求，要注意一下！
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.

Input
The first line contains 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.

The next M lines (Line 2 through M+1) each contain two integers, Pi and Ai. Pi (0 <= Pi <= 1,000) is price in cents that farmer i charges. Ai (0 <= Ai <= 2,000,000) is the amount of milk that farmer i can sell to Merry Milk Makers per day.

Output
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 Input
100 5 5 20 9 40 3 10 8 80 6 30

Sample Output
630

拜托了！各位大哥大姐！

很简单啊,先买最便宜,在买次便宜的,...,一直到数量够了

按楼上所说的，3 10 这是第一组数据，5 20 这是第二组数据，6 30这是第三组数据，这时该如何选择啊？选8 80吗？那么总数超过了100，而另为一组的结果大于输出的结果。

也觉得用贪心应该可以搞定的.
先排序(按单价从小到大)
每次选单价最小的.同时判断是否已经够了.

问一下楼主这个题目的出处?

这是在我们的课程网站上的。那里有很多 的题目啊。我也不知道老师是在那里找到的。

谢谢了！我试一试吧！

感觉有点像ACM的题目...