题解 | #24点游戏算法#

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

vector<double>a(4);
bool flag = false;
vector<bool>used(4,false);
void dfs(int p, double res){
    if(flag) return;
    if(p == 4) {
        if(res == 24) {
            flag = true;
            return;
        }
    }
    for(int i = 0; i < 4; i++){
        if(used[i] == true) continue;
        used[i]=true;
        dfs(p + 1, res + a[i]);
        dfs(p + 1, res - a[i]);
        dfs(p + 1, res * a[i]);
        dfs(p + 1, res / a[i]);
        used[i]=false;
    }
    
}
void solve(){
    dfs(0,0);
    flag ? cout << "true\n" : cout << "false\n";
}
int main() {
    while (cin >> a[0]>>a[1]>>a[2]>>a[3]) { // 注意 while 处理多个 case
        flag = false;
        solve();
    }
    return 0;
}
// 64 位输出请用 printf("%lld")