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2013
11-09

POJ 1384 Piggy-Bank [解题报告] Java

Piggy-Bank

问题描述 :

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!

输入:

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.

输出:

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.”.

样例输入:

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

样例输出:

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.

解题代码:

//* @author: ccQ.SuperSupper
import java.io.*;
import java.util.*;
class Coin{
	int price,weight;
}
public class Main {
 static final int N = 500+10,M = 10000+10;
 static int DP[] = new int[M],n,m;
 static Coin coin[] =new Coin[N];
 static void start(){
	for(int i=0;i< N;++i){
		coin[i] =new Coin();
	}
}

 public static void main(String[]args) throws Exception{
  int t,i,j;
  start();
  StreamTokenizer cin = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));
   t = Get_Num(cin);
   while(t--!=0){
	i = Get_Num(cin);
	j = Get_Num(cin);
	m = j-i;
	n = Get_Num(cin);
	for(i=0;i< n;++i){
		coin[i].price = Get_Num(cin);
		coin[i].weight = Get_Num(cin);
	}
	solve();
	if(DP[m]==-1) System.out.println("This is impossible.");
       else System.out.println("The minimum amount of money in the piggy-bank is "+DP[m]+".");
    }
  }

 static int Get_Num(StreamTokenizer cin)throws Exception{
	cin.nextToken();
	return (int) cin.nval;
}
static void solve(){
  int i,j;
  for(i=0;i<=m;++i) DP[i] = -1;
   DP[0] = 0;
   for(i=0;i< n;++i){
	for(j=0;j<=m;++j) if(DP[j]>-1 && j+coin[i].weight<=m){
	  DP[j+coin[i].weight] = Min(DP[j+coin[i].weight],DP[j]+coin[i].price);
	}
   }
}

  static int Min(int a,int b){
   if(a==-1) return b;
   return a< b?a:b;
  }
}

  1. 算法是程序的灵魂,算法分简单和复杂,如果不搞大数据类,程序员了解一下简单点的算法也是可以的,但是会算法的一定要会编程才行,程序员不一定要会算法,利于自己项目需要的可以简单了解。

  2. 第二种想法,我想来好久,为啥需要一个newhead,发现是把最后一个节点一直返回到嘴上面这层函数。厉害,这道题之前没样子想过。