Simple chat bot inputs

Newbie question!

I am still new to the whole structure of an artificial neural network, and I have one question: if I have a chatbot, what would I want its input size to be? Is that something I can change each time it runs through the network, or does the amount of inputs need to stay the same?

For instance: could I input a sentence as a list? [ [firstWord], [secondWord], [thirdWord], … [nthWord] ]
Or would it be better to put in the sentence as a 1x1 array [ [sentence] ]?

Thank you all!

Just to add: I am mapping each English word (I found a .txt file of 300k English words and mapped them to a dictionary type with a unique number for the key) For instance, a sentence “The black bear eats” would enter in as [2300, 40, 42, 60] or something like that