hdu 1114 Piggy-Bank

Problem Description

Before ACM can do anything, a budget must be prepared and the necessary financial support obtained. The main income for this action comes from Irreversibly Bound Money (IBM). The idea behind is simple. Whenever some ACM member has any small money, he takes all the coins and throws them into a piggy-bank. You know that this process is irreversible, the coins cannot be removed without breaking the pig. After a sufficiently long time, there should be enough cash in the piggy-bank to pay everything that needs to be paid. 

But there is a big problem with piggy-banks. It is not possible to determine how much money is inside. So we might break the pig into pieces only to find out that there is not enough money. Clearly, we want to avoid this unpleasant situation. The only possibility is to weigh the piggy-bank and try to guess how many coins are inside. Assume that we are able to determine the weight of the pig exactly and that we know the weights of all coins of a given currency. Then there is some minimum amount of money in the piggy-bank that we can guarantee. Your task is to find out this worst case and determine the minimum amount of cash inside the piggy-bank. We need your help. No more prematurely broken pigs! 

 

Input

The input consists of T test cases. The number of them (T) is given on the first line of the input file. Each test case begins with a line containing two integers E and F. They indicate the weight of an empty pig and of the pig filled with coins. Both weights are given in grams. No pig will weigh more than 10 kg, that means 1 <= E <= F <= 10000. On the second line of each test case, there is an integer number N (1 <= N <= 500) that gives the number of various coins used in the given currency. Following this are exactly N lines, each specifying one coin type. These lines contain two integers each, Pand W (1 <= P <= 50000, 1 <= W <=10000). P is the value of the coin in monetary units, W is it's weight in grams. 

 

Output

Print exactly one line of output for each test case. The line must contain the sentence "The minimum amount of money in the piggy-bank is X." where X is the minimum amount of money that can be achieved using coins with the given total weight. If the weight cannot be reached exactly, print a line "This is impossible.". 

 

Sample Input

3 10 110 2 1 1 30 50 10 110 2 1 1 50 30 1 6 2 10 3 20 4

 

Sample Output

The minimum amount of money in the piggy-bank is 60. The minimum amount of money in the piggy-bank is 100. This is impossible.

 

代码：

#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int E,F;
        scanf("%d%d",&E,&F);
        int n,i,v[550],w[550],f[10000];         //数组v用来记录硬币的重量，w用来记录价值
        scanf("%d",&n);
        f[0]=0;                                                 //次处只初始化f[0]=0，下面还有
        for(i=1; i<=F; i++)
            f[i]=1000000;                                    //因为是要求装满时的的最小值，所除了f[0]初始化为0外，其他要初始化为无穷大这里1000000足够了
                                                                    //有些题是要求最大值，初始化要为无穷小，这里要注意下
        for(i=1; i<=n; i++)
            scanf("%d%d",&w[i],&v[i]);

        for(i=1; i<=n; i++)
            for(int vv=v[i]; vv<=F-E; vv++)
                f[vv]=min(f[vv],f[vv-v[i]]+w[i]);        //这两个for循环是关键，一般的背包问题都是这样解决，具体问题具体分析

        if(f[F-E]!=1000000)                            //这里用了一个小技巧，有点水了，不知道别人是怎么写的，推荐还是不要我这样写
            printf("The minimum amount of money in the piggy-bank is %d.
",f[F-E]);
        else printf("This is impossible.
");
    }


    return 0;
}