I was playing a casual game of Sudoku today when a friend came by and asked "What's the hardest game of Sudoku possible?"
My response: "A Sudoku puzzle with the minimal amount of starting numbers where the puzzle is still solvable."
However, I am not happy with this because I want to know the actual minimum to the amount of starting squares I can have. Of course, position matters as well, so I will assume you can place the numbers wherever for optimization.
The closest I can do is look at individual situations to see if they are solvable. But even when I do that, I don't know if there is a setup with even less starting numbers?
Q1: What is the least amount of starting numbers required for a game of Sudoku to be solvable?
Q2: How would you define the "hardest" game of Sudoku?