In his section talking about the brute force method of solving the puzzle, he seriously overestimates the number of possibilities for the whole puzzle. Example

In his section talking about the brute force method of solving the puzzle, he seriously overestimates the number of possibilities for the whole puzzle. Example: For grid2, he lists square A2 as having 4 possibilities (1679) and A3 as having 5 possibilities (12679). Which is true, if you ignore the rules of sudoku. Specifically, not all of those combinations are worth trying. If you choose a 1 for square A2, you would not choose a 1 for square A3. Wikipedia lists there as being 10^21 unique sudoku puzzles, which is many orders of magnitude smaller than his listed 10^38 different combinations for grid2. In short, I think a proper brute force method would be significantly faster than what he initially thought it would be.