题解 | #24点运算#

本人菜鸡方法比较笨主要是用递归，一上来将输入的转为String数组方便递归，并判断是否有大小王，若有大小王直接输出ERROR并结束，若无大小王先对四张牌递归排序获得所有排列方式，再对排序过的四张牌递归插入运算符，并获得所有排列方式，并放入集合中。最后对集合遍历并计算结果，若结果为24输出结果并结束遍历

import java.util.*;

public class Main{

static List<String> anssList = new ArrayList<String>();
public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    List<String> list = new ArrayList<String>();
    while(sc.hasNext()){
        list.add(sc.next());
    }
    boolean status = true;
    String[] str = new String[list.size()];
    for (int i = 0; i < str.length; i++) {
        if(list.get(i).equals("joker") || list.get(i).equals("JOKER")){
            System.out.println("ERROR");
            status = false;
        }
        str[i] = list.get(i);
    }
    if(status){
        Integer[] i = new Integer[list.size()];
        boolean r = false;
        String[] chars = new String[]{"+", "-", "*", "/"};
        List<String[]> intList = new ArrayList<String[]>();
        getInts(str, 0, new String[i.length], intList);
        intList.forEach(k -> {
            getAns(k, 0 ,chars , "");
        });
        int temp = 0;
        if(anssList.size() != 0){
            for (int i1 = 0; i1 < anssList.size(); i1++) {
                if(getSum(anssList.get(i1)) == 24){
                    System.out.println(anssList.get(i1));
                    i1 =  anssList.size();
                }
                temp ++;
            }
        }
        if (temp == anssList.size()) System.out.println("NONE");
    }
}
static Integer getNumber(String c){
    Integer num = null;
    c = c.replace(" ", "");
    try {
        switch(c){
            case "A":
                num = 1;
                break;
            case "J":
                num = 11;
                break;
            case "Q":
                num = 12;
                break;
            case "K":
                num = 13;
                break;
            default:
                num = Integer.parseInt(c);
                break;
        }
    } catch (NumberFormatException e) {
        num = null;
    }
    return num;
}
static Integer getSum(String str){
    Integer ans = 0;
    String[] strs = new String[7];
    for (int i = 0; i < strs.length; i++) {
        strs[i] = str.substring(i, i + 1);
    }
    for (int i = 0; i + 2 < strs.length; i += 2) {
        Integer a = getNumber(strs[i]);
        Integer b = getNumber(strs[i + 2]);
        if(a == null || b == null){
            return null;
        }
        int sum1 = getSum1(a, b, String.valueOf(strs[i + 1]));
        if(i >= 4){
            ans = sum1;
        }
        else {
            strs[i + 2] = sum1 + "";
        }
    }
    return ans;
}
static Integer getSum1(Integer a, Integer b, String c){
    Integer ans = 0;
    if(c.equals("+")){
        ans = a + b;
    }
    if(c.equals("-")){
        ans = a - b;
    }
    if(c.equals("*")){
        ans = a * b;
    }
    if(c.equals("/")){
        ans = a / b;
    }
    return ans;
}
static void getInts(String[] is, int k, String[] ans, List<String[]> intList){
    String[] newAns = new String[ans.length];
    for (int i = 0; i < newAns.length; i++) {
        newAns[i] = ans[i];
    }
    for (int i = 0; i < is.length; i++) {
        newAns[k] = is[i];
        if(1 == is.length){
            intList.add(newAns);
        }
        else {
            int temp = k + 1;
            String[] ints1 = coypInts(is, i);
            getInts(ints1, temp, newAns, intList);
        }
    }
}
static void getAns(String[] is, int k, String[] chars, String ans){
    for(int i = k; i < is.length;){
        ans += is[i];
        String anss = String.valueOf(ans);
        if(i == is.length - 1 && anss.length() == 7){ 
            anssList.add(anss);
        }
        i++;
        if(i < is.length){
            for (int j = 0; j < chars.length; j++) {
                String anss1 = String.valueOf(anss);
                anss1 += chars[j];
                getAns(is, i, chars, anss1);
            }
        }
    }
}
static String[] coypInts(String[] chars, int i){
    String[] c = new String[chars.length - 1];
    Integer count = 0;
    for (int i1 = 0; i1 < chars.length; i1++) {
        if(i1 != i){
            c[count++] = chars[i1];
        }
    }
    return c;
}
static String[] coypChars(String[] chars, int i){
    String[] c = new String[chars.length - 1];
    int count = 0;
    for (int i1 = 0; i1 < chars.length; i1++) {
        if(i1 != i){
            c[count++] = chars[i1];
        }
    }
    return c;
}

}