There are more than a few techniques to solve a Sudoku puzzle ... and can get players far into more difficult puzzles before ...

Naked single and Hidden single are powerful and fast techniques to solve Sudoku but they don't guarantee solution to every sudoku. Backtracking is time consuming but surely solves every sudoku.

The key represents a square on the sudoku board (starting top left, going right then to the next row ect) and the list represents the possible values that could go in this square. When logical solve ...