A sudoku solver

This method prints one row of the puzzle, translating zero values to “.” and nonzero values to the corresponding digit, printing an extra space between each column.

It also adds an extra two spaces between columns 2 and 3, and again between columns 5 and 6. The logic that dictates these extra columns is exactly the same as the logic for blank lines between rows in Section 7.4, “Inspection: SudokuSolver.write()”.