Probalility Birthaday a Paradox

I was goimg through the probability section. I came across Birthaday a Paradox.
I totally agree with the solution the complimentary method. Probability of birthadates not colliding and taking complement.
But, I want to understand how can I calculate the probability with general method.
i.e., possible event / All events.
Can anyone help me understand this?

This article covers how to compute the probability in general: