杭电OJ1114----------------Piggy-Bank ~完全背包~

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.
   
   
   
   

这是一个完全背包的问题，并且输出的是最小的情况

所以就把结果数组中每个数都先都置成较大的值，然后再把第一个赋成0；用min来逐个的，，正向的比较更新

关键步骤：

for i=1..N

        f[v]=max{f[v],f[v-c[i]]+w[i]}

因为需要的是最小的情况，所以把MAX换为MIN

IMPOSSIBLE 的情况是最后数组中最后一个值并没有更新，所以判断一下然后输出IMPOSSIBLE即可，注意这里不能用int_max，因为这个数一加会越界变成负值，导致一系列比较出现错误！

代码：

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int main()
{
	int T;	cin>>T;
	const int INF = 1000000001;
	while(T--)
	{
		int E,F,N;
		cin>>E>>F>>N;
		vector<int>P(N+1);
		vector<int>W(N+1);
		vector<int>f(F-E+1,INF);
		f[0]=0;
		for(int i=1;i<=N;i++)
			cin>>P[i]>>W[i];
		for(int i=1;i<=N;i++)
			for(int v=W[i];v<=F-E;v++)
				f[v]=min(f[v],f[v-W[i]]+P[i]);
		if(f[F-E]==INF)
			cout<<"This is impossible."<<endl;
		else
			cout<<"The minimum amount of money in the piggy-bank is "<<f[F-E]<<"."<<endl;
	}
	return 0;
}