同学帮他侄儿问我一个问题：
资源：
1、小明的钱可以购买50瓶汽水。
2、老板搞促销，两个空汽水瓶子可以换一瓶汽水。

问：小明最多能喝多少瓶汽水？

开始还楞了一下， 现在的小学题目还真不简单。不过马上给出答案：
先是50瓶，然后用50个空瓶换来25瓶，喝完后用25个空瓶换12瓶再多个空瓶，
喝完后用13个空瓶换6瓶，然后是7个空瓶换3瓶，然后是4个空瓶换2瓶，
然后是2个空瓶换1瓶，最后问老板借1个空瓶，再用2个空瓶换1瓶，
剩下来那个空瓶还给老板。所以喝到50+25+12+6+3+2+1+1=100

不过最近在学习规则引擎， 于是就想到了怎么用规则引擎来实现。
我的想法是：
1: 假设汽水一元一瓶， 则小明最初有50元。
2: 如果兜里有超过一元钱， 则买一瓶汽水喝， 此时：
钱减少一元，同时拥有的空瓶增加一个。
3: 如果拥有至少两个空瓶， 则两个空瓶卖给老板， 兜里的钱加一。
根据如上想法， 有了如下规则引擎的实现的实现(Drool)：

java文件SodaWater.java：

Java代码

1. package org.drools.examples; 
2.  
3. import java.io.InputStreamReader; 
4. import java.io.Reader; 
5.  
6. import org.drools.FactHandle; 
7. import org.drools.RuleBase; 
8. import org.drools.RuleBaseFactory; 
9. import org.drools.StatefulSession; 
10. import org.drools.WorkingMemory; 
11. import org.drools.compiler.PackageBuilder; 
12. import org.drools.rule.Package; 
13.  
14. public class SodaWater 
15. { 
16.     public static final void main(String[] args) throws Exception { 
17.         final PackageBuilder builder = new PackageBuilder(); 
18.         builder.addPackageFromDrl( new InputStreamReader( SodaWater.class.getResourceAsStream( "SodaWater.drl" ) ) ); 
19.  
20.         final RuleBase ruleBase = RuleBaseFactory.newRuleBase(); 
21. ruleBase.addPackage( builder.getPackage() );
22.  
23.         final StatefulSession session = ruleBase.newStatefulSession(); 
24.  
25.         Customer customer = new Customer( "XiaoMing", 50); 
26.         session.insert(customer); 
27.         session.fireAllRules(); 
28.     } 
29.     
30.     public static class Customer 
31.     { 
32.         private String name; 
33.         
34.         private int money; 
35.         
36.         private int drinkSum; 
37.         
38.         private int blankCup; 
39.         
40.         public Customer(String name, int money) 
41.         { 
42.             this.name = name; 
43.             this.money = money; 
44.             this.drinkSum = 0; 
45.             this.blankCup = 0; 
46.         }        
47.  
48.         public int getMoney() 
49.         { 
50.             return money; 
51.         } 
52.         
53.         public void setMoney(int money) 
54.         { 
55.             this.money = money; 
56.         } 
57.         
58.         public int getBlankCup() 
59.         { 
60.             return blankCup; 
61.         } 
62.  
63.         public void setBlankCup(int blankCup) 
64.         { 
65.             this.blankCup = blankCup; 
66.         } 
67.  
68.         public int getDrinkSum() 
69.         { 
70.             return drinkSum; 
71.         } 
72.  
73.         public void setDrinkSum(int drinkSum) 
74.         { 
75.             this.drinkSum = drinkSum; 
76.         } 
77.  
78.         public String getName() 
79.         { 
80.             return name; 
81.         } 
82.  
83.         public void setName(String name) 
84.         { 
85.             this.name = name; 
86.         }       
87.         
88.     } 
89. } 

package org.drools.examples;

import java.io.InputStreamReader;
import java.io.Reader;

import org.drools.FactHandle;
import org.drools.RuleBase;
import org.drools.RuleBaseFactory;
import org.drools.StatefulSession;
import org.drools.WorkingMemory;
import org.drools.compiler.PackageBuilder;
import org.drools.rule.Package;

public class SodaWater
{
    public static final void main(String[] args) throws Exception {
        final PackageBuilder builder = new PackageBuilder();
        builder.addPackageFromDrl( new InputStreamReader( SodaWater.class.getResourceAsStream( "SodaWater.drl" ) ) );

        final RuleBase ruleBase = RuleBaseFactory.newRuleBase();
        ruleBase.addPackage( builder.getPackage() );

        final StatefulSession session = ruleBase.newStatefulSession();

        Customer customer = new Customer( "XiaoMing", 50);
        session.insert(customer);
        session.fireAllRules();
    }
   
    public static class Customer
    {
        private String name;
       
        private int money;
       
        private int drinkSum;
       
        private int blankCup;
       
        public Customer(String name, int money)
        {
            this.name = name;
            this.money = money;
            this.drinkSum = 0;
            this.blankCup = 0;
        }       

        public int getMoney()
        {
            return money;
        }
       
        public void setMoney(int money)
        {
            this.money = money;
        }
       
        public int getBlankCup()
        {
            return blankCup;
        }

        public void setBlankCup(int blankCup)
        {
            this.blankCup = blankCup;
        }

        public int getDrinkSum()
        {
            return drinkSum;
        }

        public void setDrinkSum(int drinkSum)
        {
            this.drinkSum = drinkSum;
        }

        public String getName()
        {
            return name;
        }

        public void setName(String name)
        {
            this.name = name;
        }      
       
    }
}

rule文件：

Sql代码

1. package org.drools.examples 
2.  
3. dialect "mvel" 
4.  
5. import org.drools.examples.SodaWater.Customer 
6.   
7.  
8. rule "buy a soda water and drink" 
9.     when 
10.         $c : Customer(money > 0, $m:money, $b:blankCup, $d:drinkSum) 
11.     then 
12.         $c.money = $m - 1; 
13.         $c.blankCup = $b + 1; 
14.         $c.drinkSum = $d + 1; 
15.         System.out.println( "Customer " + $c.name + " now buy a soda water and drink: money=" + $c.money + " and blankCup=" + $c.blankCup); 
16.         update($c); 
17. end 
18.  
19. rule "sale blank cup and get money" 
20.     when 
21.         $c : Customer(blankCup > 1, $b:blankCup, $m:money ) 
22.     then 
23.         $c.blankCup = $b - 2; 
24.         $c.money = $m + 1; 
25.         System.out.println("Customer " + $c.name + " now sale 2 cups and get money: money=" + $c.money + ", blankCup=" + $c.blankCup); 
26.         update($c); 
27. end 
28.  
29. rule "finish drink"            
30.     no-loop true    
31.     dialect "java" 
32.     when 
33.         $c : Customer(blankCup < 2, money == 0) 
34.     then 
35.         System.out.println( "Customer " + $c.getName() + " finished drink, and drink number is " + $c.getDrinkSum() + " blankCup=" + $c.getBlankCup()); 
36. end 

package org.drools.examples

dialect "mvel"

import org.drools.examples.SodaWater.Customer
 

rule "buy a soda water and drink"
    when
        $c : Customer(money > 0, $m:money, $b:blankCup, $d:drinkSum)
    then
        $c.money = $m - 1;
        $c.blankCup = $b + 1;
        $c.drinkSum = $d + 1;
        System.out.println( "Customer " + $c.name + " now buy a soda water and drink: money=" + $c.money + " and blankCup=" + $c.blankCup);
        update($c);
end

rule "sale blank cup and get money"
    when
        $c : Customer(blankCup > 1, $b:blankCup, $m:money )
    then
        $c.blankCup = $b - 2;
        $c.money = $m + 1;
        System.out.println("Customer " + $c.name + " now sale 2 cups and get money: money=" + $c.money + ", blankCup=" + $c.blankCup);
        update($c);
end

rule "finish drink"           
    no-loop true   
    dialect "java"
    when
        $c : Customer(blankCup < 2, money == 0)
    then
        System.out.println( "Customer " + $c.getName() + " finished drink, and drink number is " + $c.getDrinkSum() + " blankCup=" + $c.getBlankCup());
end

运行结果如下：
Customer XiaoMing now buy a soda water and drink: money=49 and blankCup=1
Customer XiaoMing now buy a soda water and drink: money=48 and blankCup=2
Customer XiaoMing now sale 2 cups and get money: money=49, blankCup=0
Customer XiaoMing now buy a soda water and drink: money=48 and blankCup=1
Customer XiaoMing now buy a soda water and drink: money=47 and blankCup=2

...

Customer XiaoMing now buy a soda water and drink: money=1 and blankCup=1
Customer XiaoMing now buy a soda water and drink: money=0 and blankCup=2
Customer XiaoMing now sale 2 cups and get money: money=1, blankCup=0
Customer XiaoMing now buy a soda water and drink: money=0 and blankCup=1
Customer XiaoMing finished drink, and drink number is 99 blankCup=1

不过小明最后手上还有最后一个瓶子， 计算机只能到此了。
向老板借一个瓶子换一瓶汽水，喝完在还一个空瓶子，估计就是人类智慧来。

此程序需要drools的jar包，具体可见：

http://lcllcl987.iteye.com/blog/254381

看看大家还有什么好的算法。