题解 | #24点运算#

不懂算法，就是瞎做，按着数学的思想，把思路变成代码，等刷完题再好好学学算法，整点高大上的名词

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息

public class Main {

      private static String[]  opt = new String[]{"","",""};

    private static HashMap<String,String> sMaps = new HashMap<>();

    private static List<String> sResults = new ArrayList<>();

    public static void main(String[] args) {

        Scanner s = new Scanner(System.in);

        String[] lines = s.nextLine().trim().split(" ");

        for (int i =0;i<lines.length;i++){

            if (lines[i].equalsIgnoreCase("J")){

                lines[i] = "11";

                sMaps.put(lines[i],"J");

            }else if (lines[i].equalsIgnoreCase("Q")){

                lines[i]="12";

                sMaps.put(lines[i],"Q");

            }else if (lines[i].equalsIgnoreCase("K")){

                lines[i]="13";

                sMaps.put(lines[i],"K");

            }else if (lines[i].equalsIgnoreCase("A")){

                lines[i]="1";

                sMaps.put(lines[i],"A");

            }else{

                sMaps.put(lines[i],lines[i]);

            }

           if (lines[i].equalsIgnoreCase("joker")){

               System.out.println("ERROR");

               return;

           }

        }

        int a = Integer.parseInt(lines[0]);

        int b = Integer.parseInt(lines[1]);

        int c = Integer.parseInt(lines[2]);

        int d = Integer.parseInt(lines[3]);

        int[] ints = new int[]{a, b, c, d};

        List<int[]> data = new ArrayList<>();

        //输出所有 a b c d可能的排列组合

        //先从0位置取数，可以取4种,依次类推

        for (int i =0;i<4;i++){

            int[] tmp = new int[4];

            tmp[0]=ints[i];

            for (int j =0;j<3;j++){

                int[] tmp1 = removeElements(ints,tmp[0]);

                tmp[1]=tmp1[j];

                for (int k=0;k<2;k++){

                    int[] tmp2 = removeElements(tmp1,tmp[1]);

                    tmp[2]=tmp2[k];

                    for (int l=0;l<1;l++){

                        int[] tmp3 =removeElements(tmp2,tmp[2]);

                        tmp[3]=tmp3[l];

                        int[] temp = new int[4];

                        temp[0]=tmp[0];

                        temp[1]=tmp[1];

                        temp[2]=tmp[2];

                        temp[3]=tmp[3];

                        data.add(temp);

                    }

                }

            }

        }

        for (int[] tmp : data){

           cal(tmp[0],tmp,1);

        }

        if (sResults.isEmpty()){

            System.out.println("NONE");

        }else{

            System.out.println(sResults.get(0));

        }

    }

    private static int[] removeElements(int[] arr,int value){

        int[] ints = new int[arr.length-1];

        int i=0;

        boolean first=true;//第一个遇到的删除，其他的应添加到队列里

        for (int tmp : arr){

            if (value!=tmp){

                ints[i]=tmp;

                i++;

            }else{

                if (first){

                    first=false;

                }else{

                    ints[i]=tmp;

                    i++;

                }

            }

        }

        return ints;

    }

    public static int count=0;

    private static  int cal(int result,int[] ints,int index){

        if (index>=4){

            count++;

            if (result==24){

                String res ="" +getMappingString(ints[0]) +opt[0]

                        +getMappingString(ints[1])+opt[1]

                        +getMappingString(ints[2])+opt[2]

                        +getMappingString(ints[3]);

                sResults.add(res);

            }

            return result;

        }

        // System.out.println("执行加法:"+result+",index="+index);

        int add = result + ints[index];

        opt[index-1]="+";

        cal(add,ints,index+1);

        int subtract =result - ints[index];

        opt[index-1]="-";

        cal(subtract,ints,index+1);

        // System.out.println("执行减法:"+result+",index="+index);

        int times = result * ints[index];

        opt[index-1]="*";

        cal(times,ints,index+1);

        // System.out.println("执行乘法:"+result+",index="+index);

        int division =result / ints[index];

        opt[index-1]="/";

        return cal(division,ints,index+1);

    }

    private static String getMappingString(int value){

        return sMaps.get(value+"");

    }

}