题解 | #24点游戏算法#

//注意输入为double类型
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

double cal(double a, double b, int op) {
    if (op == 0) return a + b;
    else if (op == 1) return a - b;
    else if (op == 2) return a * b;
    else  return a / b;
}

bool dfs(vector<double>& nums, int op, double sum, int index, vector<int>& ops) {
    sum = cal(sum, nums[index], op);
    if (index == 3 && sum == 24) {
        return true;
    } else if (index == 3) {
        return false;
    }

    for (int i = 0; i < 4; ++i) {
        ops.push_back(i);
        if (dfs(nums, i, sum, index + 1, ops)) {
            return true;
        }
        ops.pop_back();
    }
    return false;
}

int main() {
    vector<double> nums(4);
    for (int i = 0; i < 4; ++i) {
        cin >> nums[i];
    }
    vector<int> ops;
    sort(nums.begin(), nums.end());
    while (next_permutation(nums.begin(), nums.end())) {
        for (int i = 0; i < 4; ++i) {
            ops.push_back(i);
            if (dfs(nums, i, nums[0], 1, ops)) {
                cout<<"true"<<endl;
                return 0;
            }
            ops.pop_back();
        }
    }
    cout<<"false"<<endl;
    return 0;
}