题解 | #24点运算#

暴力解法， 任何时候都能写出来

/*
 * Created by JoeTim on 2021/6/30.
 */


#include <bits/stdc++.h>
using namespace std;

// 3 4 5 6 7 8 9 10 J Q K A 2 joker JOKER
bool dfs(int abc, int d, string &res) {
  if (abc + d == 24) {
    res.push_back('+');
    return true;
  }
  if (abc - d == 24) {
    res.push_back('-');
    return true;
  }
  if (abc * d == 24) {
    res.push_back('*');
    return true;
  }
  if (abc / d == 24) {
    res.push_back('/');
    return true;
  }
  return false;
}
bool dfs(int ab, int c, int d, string &res) {
  if (dfs(ab + c, d, res)) {
    res.push_back('+');
    return true;
  }
  if (dfs(ab - c, d, res)) {
    res.push_back('-');
    return true;
  }
  if (dfs(ab * c, d, res)) {
    res.push_back('*');
    return true;
  }
  if (dfs(ab / c, d, res)) {
    res.push_back('/');
    return true;
  }
  return false;
}
bool dfs(int a, int b, int c, int d, string &res) {
  if (dfs(a + b, c, d, res)) {
    res.push_back('+');
    return true;
  }
  if (dfs(a - b, c, d, res)) {
    res.push_back('-');
    return true;
  }
  if (dfs(a * b, c, d, res)) {
    res.push_back('*');
    return true;
  }
  if (dfs(a / b, c, d, res)) {
    res.push_back('/');
    return true;
  }
  return false;
}
int main() {
  unordered_map<string, int> CARD_MAP = {
      {"A", 1}, {"2", 2}, {"3", 3}, {"4", 4}, {"5", 5}, {"6", 6}, {"7", 7}, {"8", 8}, {"9", 9}, {"10", 10}, {"J", 11},
      {"Q", 12}, {"K", 13}, {"joker", -1}, {"JOKER", -2}
  };
  unordered_map<int, string> CARD_INT_TO_STRING_MAP;
  for (auto it : CARD_MAP) {
    CARD_INT_TO_STRING_MAP[it.second] = it.first;
  }
  string s1, s2, s3, s4;
  while (cin >> s1 >> s2 >> s3 >> s4) {
    vector<int> nums = {CARD_MAP[s1], CARD_MAP[s2], CARD_MAP[s3], CARD_MAP[s4]};
    int a(CARD_MAP[s1]), b(CARD_MAP[s2]), c(CARD_MAP[s3]), d(CARD_MAP[s4]);
    if (a <= 0 || b <= 0 || c <= 0 || d <= 0) {
      cout << "ERROR" << endl;
      continue;
    }
    int target = 24;
    int cur = 0;
    string res;
    bool isFlat = false;
    for (int i = 0; i < 4; ++i) {
      if (isFlat)
        break;
      for (int j = 0; j < 4; ++j) {
        if (isFlat)
          break;
        for (int k = 0; k < 4; ++k) {
          if (isFlat)
            break;
          for (int l = 0; l < 4; ++l) {
            if (isFlat)
              break;
            if (i == j || i == k || i == l || j == k || j == l || k == l)
              continue;
            if (dfs(nums[i], nums[j], nums[k], nums[l], res)) {
              printf("%s%c%s%c%s%c%s\n",
                     CARD_INT_TO_STRING_MAP[nums[i]].c_str(),
                     res[2],
                     CARD_INT_TO_STRING_MAP[nums[j]].c_str(),
                     res[1],
                     CARD_INT_TO_STRING_MAP[nums[k]].c_str(),
                     res[0],
                     CARD_INT_TO_STRING_MAP[nums[l]].c_str());
              isFlat = true;
            }
          }
        }
      }
    }
    if (!isFlat)
      cout << "NONE" << endl;
  }
  return 0;
}