已知一副撲克牌有54張，去除大王和小王，剩餘52張。在其中隨機抽取4張牌，利用加減乘除進行計算得到24. 從A到10，他們的值分別為1到10. 從J到K，他們對應的值是減去10以後的值。編寫程式生成一副撲克牌，隨機抽取4張，進行計算是否能得到24. 如果可以，列出可能的計算表示式，可能有多種計算形式。

主要思想就是先生成除去大小王的52張撲克牌，然後從中隨機抽取四張。接著用排列組合的方式找到能計算得到24的表示式。

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");
 // 生成撲克牌
 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("抽到的撲克牌：");
 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種計算方法",count);
 }
 else {
  System.out.print("無法計算得到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){
 // 四個數字中間有三個運算子，因此用三重迴圈遍歷。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,k);
  }
  }
 }
 
 
 }
 /*
 * 分類討論
 */
 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,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,cal(num3,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,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,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,op1) == 24) {
  System.out.println(num1+symbol(op1)+"["+num2+symbol(op2)+"("+num3+symbol(op3)+num4+")]");
  count++;
 }
 }
 /*
 * 按順序計算
 */
 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;
 }
 /*
 * 將代表計算符號的數字轉換成字元存入String陣列並返回
 */
 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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