题解，严谨能过所有样例

#include<bits/stdc++.h>
using namespace std;
#define int long long
double mid;
bool find(double x,double y)
{
    double sum=x*x*x*x*2018+21*x+5*x*x*x+5*x*x+14;
    if(sum>=y)return true;
    else return false;
}
double erfen(double y)
{
    double l=0,r=100.00;
    for(int i=1;i<=100;i++)
    {
        mid=(l+r)/2;
        if(find(mid,y))r=mid;
        else l=mid;
    }
    return mid;
    
}
signed main()
{
    int T;
    cin>>T;
    while(T--)
    {
    double y;
    cin>>y;
    double ans=erfen(y);
        
    if(ans*ans*ans*ans*2018+21*ans+5*ans*ans*ans+5*ans*ans+14-y<=0.001)printf("%.4lf\n",ans);
    else cout<<-1<<endl;
    }
    
}