[ACM_HDU_1009]FatMouse' Trade(贪心算法入门)

FatMouse' Trade

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 22404 Accepted Submission(s): 6972

Description
FatMouse prepared M pounds of cat food, ready to trade with the cats guarding the warehouse containing his favorite food, JavaBean.
The warehouse has N rooms. The i-th room contains J[i] pounds of JavaBeans and requires F[i] pounds of cat food. FatMouse does not have to trade for all the JavaBeans in the room, instead, he may get J[i]* a% pounds of JavaBeans if he pays F[i]* a% pounds of cat food. Here a is a real number. Now he is assigning this homework to you: tell him the maximum amount of JavaBeans he can obtain.


Input
The input consists of multiple test cases. Each test case begins with a line containing two non-negative integers M and N. Then N lines follow, each contains two non-negative integers J[i] and F[i] respectively. The last test case is followed by two -1's. All integers are not greater than 1000.


Output
For each test case, print in a single line a real number accurate up to 3 decimal places, which is the maximum amount of JavaBeans that FatMouse can obtain.


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


Source
HDU1009


其实这道题就相当于[ACM实验三]ACM程序设计基础(1)中可分割的背包问题,所谓贪心,就是每一次都找最大价值的作为当前阶段的结果。

应该注意的是float类型相除可能出现误差,而再乘以一个比较大数将使误差扩大,导致WA,因此要用double型。

代码如下:




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posted on 2012-04-18 22:47  springside5  阅读(165)  评论(0编辑  收藏  举报