题解 | #24点运算#

#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include<algorithm>
using namespace std;

int convert(string a)
{
    if (a == "A")
    {
        return 1;
    }
    else if (a == "J")
    {
        return 11;
    }
    else if (a == "Q")
    {
        return 12;
    }
    else if (a == "K")
    {
        return 13;
    }
    else if (a == "joker" || a == "JOKER")
    {
        return -1;
    }
    else
    {
        return (a[0] - '0');
    }
}

char convert_to_input(double a)
{
    if (a == 1)
    {
        return 'A';
    }
    else if (a == 11)
    {
        return 'J';
    }
    else if (a == 12)
    {
        return 'Q';
    }
    else if (a == 13)
    {
        return 'K';
    }
    else
    {
        return (a + '0');
    }
}

double cal(double a, double b, char c) { //根据运算符运算结果
	switch (c) {
	case '+': return a + b;
	case '-': return a - b;
	case '*': return a * b;
	case '/': return a / b;
	}
	return 0;
}

bool check(vector<double>& nums) {
	char op[4] = { '+', '-', '*', '/' };
	sort(nums.begin(), nums.end()); //先按照从小到大排
	do {
		for (int i = 0; i < 4; i++)
        { //遍历三个位置的所有可能运算符
			for (int j = 0; j < 4; j++)
            {
				for (int k = 0; k < 4; k++) 
                {
					double first = cal(nums[0], nums[1], op[i]); //依次运算
					double second = cal(first, nums[2], op[j]);
					double third = cal(second, nums[3], op[k]);
					if (third == 24) //判断是否等于24
					{
                        cout << convert_to_input(nums[0]) << op[i] << convert_to_input(nums[1]) << op[j] << convert_to_input(nums[2]) << op[k] << convert_to_input(nums[3]) << endl;
                        return true;
                    }
				}
            }
        }
	} while (next_permutation(nums.begin(), nums.end())); //依次找到其他排列
	return false;
}

int main() {
    string strs;
    getline(cin ,strs);
    stringstream input(strs);

    string s;
    vector<double> NUM;
    while(input >> s)
    {
        NUM.push_back(convert(s));
    }

    if (find(NUM.begin(),NUM.end(),-1.0) != NUM.end())
    {
        cout << "ERROR";
    }
    else if (!check(NUM))
    {
        cout << "NONE";
    }
}
// 64 位输出请用 printf("%lld")