24点游戏

游戏规则：随机每次从扑克牌中抽取四张牌，使用加减乘除，第一个得到24的人赢，其中AJQK分别代表1,11,12,13.

算法分析：先定义得到有多少种算法的方法getCount()，定义产生随机数的方法createRandomWords()，显示纸牌号码 的方法showWords()将产生的随机数转化为list列表在遍历输出，定义将字符转换为double类型的方法 convertStringToDouble()，主要将AJQK转换为数字类型，最后定义回溯算法exhaustiveMethodToCards()求 得得到24的全部解

package com.jack.game;

import java.util.List;
import java.util.Random;

public class TFPGame {
	private final int cycleNum = 4;//抽取四张牌
	private final String[] OriginalCards = { "A", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"};
	private String[] randomCards = new String[cycleNum];
	private double[] number = new double[cycleNum];
	private boolean flag = false;
	private int count = 0;//计算方法的个数
	
	public int getCount(){                //得到有多少种算法
		return count;
	}
		
	public void createRandomWords(){         //定义产生随机数的方法
		Random random = new Random();         //创建对象
		
		for( int i = 0 ; i < cycleNum ; i++){
			randomCards[i] = OriginalCards[random.nextInt(OriginalCards.length)];//返回一个0到OriginalCards.length长度的随机整数，并存入数组。
		}
	}
	
	public void showWords()	{				//定义显示纸牌号码的方法
		System.out.println("随机产生的纸牌：");
		
		List<String> stringList = java.util.Arrays.asList( randomCards );//将产生的随机数数组转化为list列表
		
		for( Object str : stringList)			//遍历Stringlist
		{
			System.out.print(str + " ");
		}
		
		System.out.println();
		
	}
	
	public void convertStringToDouble()			//定义方法，主要是将A，J,Q,K转化为double类型
	{
		for( int i = 0 ; i < cycleNum ; i++)
		{
			switch( randomCards[i] )
			{
			case "A" :
				randomCards[i] = "1";
				break;
			case "J" :
				randomCards[i] = "11";
				break;
			case "Q" :
				randomCards[i] = "12";
				break;
			case "K" :
				randomCards[i] = "13";
				break;
			}
			
			number[i] = Double.parseDouble(randomCards[i]);
		}
	}
	
	public void exhaustiveMethodToCards( int n ){	//回溯算法求运算得24的所有解	
		if ( n == 1 )  {  
	        if ( Math.abs ( number[0] - 24 ) <= ( 1e-6 ) ){  //如果number【0】-24的绝对值小于10的-6次方  
	            System.out.println( randomCards[0]); 
	            count++;
	            flag = true;   
	        }  
	    } 
		else{
			for(int i=0; i < n; i++)  {  
				for (int j = i + 1; j < n; j++)  {  
					double a, b;  
					String expressiona, expressionb;  
					a = number[i];  
					b = number[j];  
					number[j] = number[n - 1];  
					expressiona = randomCards[i];  
					expressionb = randomCards[j];  
					randomCards[j] = randomCards[n - 1];  
					randomCards[i]= '('+ expressiona + '+' + expressionb + ')';  
					number[i] = a + b;  
					exhaustiveMethodToCards(n-1);  //将n-1带入方法继续执行
					randomCards[i]='('+ expressiona+ '-' + expressionb + ')';  
					number[i] = a - b;  
					exhaustiveMethodToCards(n-1);  //将n-1带入方法继续执行
					randomCards[i] = '('+expressionb + '-' + expressiona + ')';  
					number[i] = b -a;  
					exhaustiveMethodToCards(n-1);  //将n-1带入方法继续执行
					randomCards[i]= '('+ expressiona +'*'+ expressionb+ ')';  
					number[i]=a*b;  
					exhaustiveMethodToCards(n-1);  //将n-1带入方法继续执行
					
					if (b != 0)  //若b不为0，可为除数
					{  
						randomCards[i] ='('+expressiona+'/' + expressionb + ')';  
						number[i] = a / b;  
						exhaustiveMethodToCards(n-1);  //将n-1带入方法继续执行
					}  
					
					if (a != 0)  //若a不为0，可为除数
					{  
						randomCards[i]='('+expressionb + '/'+ expressiona + ')';  
						number[i] = b / a;  
						exhaustiveMethodToCards(n-1);  //将n-1带入方法继续执行
					}  
					
					number[i] =a;  
					number[j]=b;  
					randomCards[i] = expressiona;  
					randomCards[j] = expressionb;  
				}  
			} 
		}
	}
	
	public static void main(String[] args) {
		TFPGame tfp = new TFPGame();  //创建TFPGame的对象tfp
		tfp.createRandomWords();
		tfp.showWords();
		tfp.convertStringToDouble();   //调用方法
		
		System.out.println("\n计算结果如下：");
		
		tfp.exhaustiveMethodToCards(tfp.cycleNum);
		
		if ( tfp.flag == true )
		{
			System.out.println("\n总共有" + tfp.getCount() + "种算法");
		}
		else
		{
			System.out.println("\n失败！");
		}
		
	}

}