已知一副扑克牌有54张，去除大王和小王，剩余52张。在其中随机抽取4张牌，利用加减乘除进行计算得到24. 从A到10，他们的值分别为1到10. 从J到K，他们对应的值是减去10以后的值。编写程序生成一副扑克牌，随机抽取4张，进行计算是否能得到24. 如果可以，列出可能的计算表达式，可能有多种计算形式。

主要思想就是先生成除去大小王的52张扑克牌，然后从中随机抽取四张。接着用排列组合的方式找到能计算得到24的表达式。

package Poker;import java.util.Random;import java.util.Stack;public class Poker { static int count = 0; static int count_2 = 0; public static Stack<Integer> stack = new Stack<Integer>(); public static Stack<Integer> stack_temp = new Stack<Integer>(); public static Stack<String> stack_collection = new Stack<String>(); public static void main(String[] args) { System.out.println("Poker World"); // 生成扑克牌 int poker[][] = new int[4][13]; for(int i = 0; i < 4; i++) { for(int j = 0; j < 13; j++) { if(j + 1 < 11) { poker[i][j] = j+1; } else { poker[i][j] = j-9; } } } Random r = new Random(); int randomPoker[] = new int[4]; for(int i = 0; i < 4; i++) { randomPoker[i] = poker[r.nextInt(3)][r.nextInt(12)]; stack_temp.add(randomPoker[i]); } System.out.print("抽到的扑克牌："); for(int element: randomPoker) { System.out.printf("%d ", element); } System.out.print("\n"); order(randomPoker, 4, 0); //System.out.printf("%d\n",count_2); if(count != 0) { System.out.printf("共有%d种计算方法", count); } else { System.out.print("无法计算得到24"); } } private static void order(int[] poker, int targ, int cur) { // TODO Auto-generated method stub if(cur == targ) { String str = stack.toString(); if(!stack_collection.contains(str)) { stack_collection.add(str); count_2 += 1; int new_poker[] = new int[4]; for(int i = 0; i < 4; i++) { new_poker[i] = stack.pop(); } for(int i = 3; i >= 0; i--) { stack.push(new_poker[i]); } do24(new_poker); } return; } for(int i = 0; i < poker.length; i++) { if(stack_temp.contains(poker[i])) { stack.add(poker[i]); for(int j = 0; j < stack_temp.size(); j++) { if(stack_temp.get(j) == poker[i]) { stack_temp.remove(j); break; } } order(poker, targ, cur+1); stack.pop(); stack_temp.add(poker[i]); } } } public static void do24(int[] poker){ // 四个数字中间有三个运算符，因此用三重循环遍历。其中0表示+，1表示-，2表示x，3表示÷ int test[] = {1,2,3,4}; for(int i=0;i<4;i++){ for(int j=0;j<4;j++){ for(int k=0;k<4;k++){ operate(poker,i,j,k); //operate(test,i,j,k); } } } } /* * 分类讨论 */ public static void operate(int[] poker, int op1, int op2, int op3) { int num1 = poker[0]; int num2 = poker[1]; int num3 = poker[2]; int num4 = poker[3]; if((cal(cal(cal(num1,num2,op1),num3,op2),num4,op3) == 24)) { if((((op2 == 0) || (op2 == 1))&&((op3 == 0) || (op3 == 1)))||((op2 != 0) && (op2 != 1))) { System.out.println("("+num1+symbol(op1)+num2+")"+symbol(op2)+num3+symbol(op3)+num4); count++; } } else if(cal(cal(num1,cal(num2,num3,op2),op1),num4,op3) == 24) { if((((op1 == 0) || (op1 == 1))&&((op3 == 0) || (op3 == 1)))||((op1 != 0) && (op1 != 1))) { System.out.println(num1+symbol(op1)+"("+num2+symbol(op2)+num3+")"+symbol(op3)+num4); count++; } else { System.out.println("["+num1+symbol(op1)+"("+num2+symbol(op2)+num3+")]"+symbol(op3)+num4); count++; } } else if(cal(cal(num1,num2,op1),cal(num3,num4,op3),op2) == 24) { if((((op1 == 0) || (op1 == 1))&&((op2 == 0) || (op2 == 1)))||((op1 != 0) && (op1 != 1))) { System.out.println(num1+symbol(op1)+num2+symbol(op2)+"("+num3+symbol(op3)+num4+")"); count++; } else { System.out.println("("+num1+symbol(op1)+num2+")"+symbol(op2)+"("+num3+symbol(op3)+num4+")"); count++; } } else if(cal(cal(cal(num1,num2,op1),num3,op2),num4,op3) == 24) { if((((op1 == 0) || (op1 == 1))&&((op2 == 0) || (op2 == 1)))||((op1 != 0) && (op1 != 1))) { System.out.println("("+num1+symbol(op1)+num2+symbol(op2)+num3+")"+symbol(op3)+num4); count++; } else { System.out.println("[("+num1+symbol(op1)+num2+")"+symbol(op2)+num3+"]"+symbol(op3)+num4); count++; } } else if(cal(num1,cal(cal(num2,num3,op2),num4,op3),op1) == 24) { if((((op2 == 0) || (op2 == 1))&&((op3 == 0) || (op3 == 1)))||((op2 != 0) && (op2 != 1))) { System.out.println(num1+symbol(op1)+"("+num2+symbol(op2)+num3+symbol(op3)+num4+")"); count++; } else { System.out.println(num1+symbol(op1)+"[("+num2+symbol(op2)+num3+")"+symbol(op3)+num4+"]"); count++; } } else if(cal(num1,cal(num2,cal(num3,num4,op3),op2),op1) == 24) { System.out.println(num1+symbol(op1)+"["+num2+symbol(op2)+"("+num3+symbol(op3)+num4+")]"); count++; } } /* * 按顺序计算 */ public static double cal(double num1,double num2,int num){ double sum=0.0; switch(num) { case 0: sum = num1 + num2; break; case 1: sum = num1 - num2; break; case 2: sum = num1 * num2; break; case 3: if(num1 % num2 == 0) { sum = num1 / num2; } else { sum = 999; } break; default: break; } return sum; } /* * 将代表计算符号的数字转换成字符存入String数组并返回 */ public static String symbol(int symbolNum){ String symbol = ""; switch (symbolNum) { case 0: symbol="+"; break; case 1: symbol="-"; break; case 2: symbol="x"; break; case 3: symbol="÷"; break; default: break; } return symbol; }}

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