题解 | #24点运算#

import java.util.HashMap;
import java.util.Scanner;

public class Main {

    static HashMap<String, Integer> map = new HashMap<String, Integer>() {
        {
            put("A", 1);
            put("2", 2);
            put("3", 3);
            put("4", 4);

            put("5", 5);
            put("6", 6);
            put("7", 7);

            put("8", 8);
            put("9", 9);
            put("10", 10);

            put("J", 11);
            put("Q", 12);
            put("K", 13);

        }
    };


    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner sc = new Scanner(System.in);
        String input = sc.nextLine();
        if (input.contains("joker") || input.contains("JOKER")) {
            System.out.println("ERROR");
        } else {
            String[] arr = input.split(" ");



            if (dfs(arr, new int[] {1, 0, 0, 0}, arr[0], map.get(arr[0]))
                    || dfs(arr, new int[] {0, 1, 0, 0}, arr[1], map.get(arr[1]))
                    || dfs(arr, new int[] {0, 0, 1, 0}, arr[2], map.get(arr[2]))
                    || dfs(arr, new int[] {0, 0, 0, 1}, arr[3], map.get(arr[3]))
               ) {

            } else {
                System.out.println("NONE");
            }
        }
    }

    static boolean dfs(String[] arr, int[] visited, String func, int curVal) {

        int sum = 0;
        for (int i = 0; i < 4; i++) {
            sum += visited[i];
        }

        if (curVal == 24 & sum == 4) {
            System.out.println(func);
            return true;
        }


        for (int i = 0; i < 4; i++) {
            if (visited[i] == 0) {
                visited[i] = 1;



                if (dfs(arr, visited.clone(), func + "+" + arr[i], curVal + map.get(arr[i]))) {
                    return true;
                }




                if (dfs(arr, visited.clone(), func + "-" + arr[i], curVal - map.get(arr[i]))) {
                    return true;
                }



                if (dfs(arr, visited.clone(), func + "*" + arr[i], curVal * map.get(arr[i]))) {
                    return true;
                }




                if (dfs(arr, visited.clone(), func + "/" + arr[i], curVal / map.get(arr[i]))) {
                    return true;
                }

                visited[i] = 0;
            }
        }
        return false;
    }


}