题解 | #24点游戏算法#

#include <iostream>
#include <vector>
using namespace std;

bool dfs(vector<int>& arr, vector<bool>& used, int k, double res){
    if(k==4&&res==24) return true;
    if(k==4&&res!=24) return false;
    bool ret = false;
    for(int i=0;i<4;i++){
        if(!used[i]){
            int n = arr[i];
            used[i] = true;
            ret|=dfs(arr, used, k+1, res+n);
            ret|=dfs(arr, used, k+1, res-n);
            ret|=dfs(arr, used, k+1, res*n);
            ret|=dfs(arr, used, k+1, res/n);
            used[i] = false;
        }
    }
    return ret;
}

int main() {
    vector<int> num(4);
    while (cin>>num[0]>>num[1]>>num[2]>>num[3]) {
        vector<bool> used(4, false);
        bool ret = dfs(num, used, 0, 0);
        cout<<(ret?"true":"false")<<endl;
    }
}