分解质因数 90 = 2 * 3 * 3 * 5

vector<int> func(int n) {
    vector<int> ans;
    
    int i;
    while (n != 1) {
        i = 2;
        
        while (1) {
            if (n % i == 0) {
                ans.push_back(i);
                std::cout << i;
                n /= i;
                break;
            }
            i++;
        }
        if (n != 1) {
            std::cout << " * ";
        }
    }
    return ans;
}