What is Sudoku?

Sudoku, a popular logic game, traditionally consists of a 9x9 square grid subdivided into smaller 3x3 grids, known as 'blocks' or 'boxes'. Each row, column, and block contains nine cells. Bellow is an example of an empty Sudoku board.

The goal of the game is to fill these cells with numbers from 1 to 9, ensuring that each number appears only once in every row, column, and block, as demonstrated in the completed Sudoku board below.

At the start of a Sudoku game, some numbers are provided as clues. The challenge lies in filling the empty cells based on these initial numbers. Bellow is an example of a Sudoku board with some numbers provided as clues.

Sudoku's difficulty ranges from very easy to extremely hard, making it a perfect brain exercise and relaxation tool, enjoyed by enthusiasts worldwide.

What Makes a Good Sudoku Puzzle?

A valid Sudoku puzzle must be solvable - that is, there should be a way to fill the cells that meets the basic criteria of the game.

The key attributes of a quality Sudoku puzzle are:

Uniqueness of Solution: An ideal Sudoku puzzle has a unique solution. There should be only one correct way to fill in the grid. This assumption is key for players and forms the basis of many solving strategies.
Logical Solvability: A puzzle should be solved through logical reasoning, not by guesswork or trial and error. Puzzles designed for humans should offer logical deductions, distinguishing them from those generated for computer algorithms, which might require guessing.
Appropriate Difficulty: A puzzle's difficulty should match the player's skill level. It's not about being the hardest or easiest, but providing a clear difficulty rating so players can choose the right challenge. Difficulty often relates to the number of pre-filled numbers, but a skilled designer knows how to balance this with the puzzle's complexity.

Basic Sudoku Solving Techniques

Here are some foundational techniques in solving Sudoku:

Full House

This technique involves identifying the missing number in a nearly complete row, column, or block.

Last Remaining Cell

This technique can be used when all empty cells but one can be excluded by the numbers already present in corresponding rows, columns, and blocks.

Last Possible Number

This method is used when a cell can only accommodate one specific number, given the numbers already present in its row, column, and block.

Note Taking

This technique involves writing down all possible numbers for each cell, then eliminating them as you go.

For additional Sudoku solving techniques, refer to our continually updated tutorials.