Should I notify the teacher that he accidentally gave out the answers to an assignment? For one of my class projects, the teacher coded the entire solution, then took out a few sections that we are supposed to complete for our assignment. This incomplete code was distributed to the class as a starting point. When he was writing the solution, he used source control. He forgot to delete his repository, so all of his commits are there... You can checkout the commits to get the full solution. I don't think he is aware of it, because he hasn't brought it up in class.

I found this while I was working on my solution. Once I found it, it was difficult to find a different path to the solution. I think my solution is dissimilar, but I feel I am playing a dangerous game here.

I'm not sure what I should do here. I could choose to not tell him and hope they don't catch it, or I could choose to tell him and basically admit I had access to the solution while I was working on it.
Send him a polite email explaining that, while you completed the assignment on your own (which I am assuming to be true), by stumbling upon the solutions in advance you had a hard time doing anything different. Professors are people--he should recognize his mistake and appreciate that you were forthcoming. Chances are he'll reassign the project or discount its weight toward your grade and just tell people to review it anyway because you need to know the material. The sooner you say something the better though. Indeed, after a while it may look like you were trying to hide it from him.