FatMouse' Trade
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others) Total Submission(s): 34126 Accepted Submission(s): 11152
Problem 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
Author
CHEN, Yue
Source
Recommend
JGShining
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct sss
{
double x;
double y;
double z;
}sss;
struct sss a[1010];
int cmp(const void *a,const void *b)
{
sss *c=(sss *)a;
sss *d=(sss *)b;
return c->z>d->z?1:-1;
}
int main()
{
int m,n;
while(scanf("%d %d",&m,&n),(n!=-1||m!=-1))
{
int i;
double toal=0;
for(i=0;i<n;i++)
{
scanf("%lf %lf",&a[i].x,&a[i].y);
a[i].z=a[i].x/a[i].y;
}
qsort(a,n,sizeof(a[0]),cmp);
for(i=n-1;i>=0;i--)
{
if(m<=a[i].y)
{
toal+=a[i].x*m/a[i].y;
break;
}
else
{
toal+=a[i].x;
m-=a[i].y;
}
}
printf("%.3lf
",toal);
}
return 0;
}
先理解一下题意：老鼠和猫交易，规则很简单，每个仓库里有J[i]磅鼠食，如果全部换走这些，老鼠需要F[i]磅猫食，当然老鼠也不用把一个仓库里的鼠食全部换走，可以按比例来换，比如
5 3
7 2
4 3
5 2
意思就是老鼠有5磅猫食，先用2磅猫食换7磅鼠食（7 2），然后还剩3磅猫食，再用2磅猫食换5磅鼠食（5 2），还剩1磅，然后换1.33磅（4*1/3），所以一共最多换13.333磅鼠食。
理解了意思就好做了，一看就是贪心算法，肯定要排序。排序时要注意，输入的J[i]F[i]一定用double不然的话计算结果double z=J[i]/f[i]是整型，我的就是那种情况，这和书上讲的不太一样，好像用int型时它只是把结果转换成了double型。