unity - Check if all gameobjects are destroyed

I am making a shooting game, where I have a countdown as I destroy enemies. I want to implement logic when all the game objects are destroyed within the given time, and the countdown reaches zero.

How do I do that?

Answer

You need to find a way of identifying all objects of interest. Do they have a particular script on them? You simply count them

if(GameObject.FindObjectOfType()==null)
{
    // Everything destroyed
}
else
{
    // Something survived

}