Beginner Sudoku Guide: Learn the basic rules of Sudoku and Beginner Strategies

Sudoku rules

What is the overall goal of Sudoku?

Sudoku is a puzzle game using numbers that can be solved entirely with numbers 1 to 9 and logic. It is important to remember that since these are logical puzzles, no guessing is allowed to find which number should be assigned to a cell. Well designed Sudoku puzzles only have one unique solution.

What are the rules of Sudoku?

  • The game is played on a 9x9 grid that is further broken down into 3x3 blocks (nonet).
  • Players can only enter numbers from 1 to 9 into each cell on the grid.
  • Each row must be filled in with the numbers 1 to 9 without duplicates.
  • Each column must be filled in with numbers 1 to 9 without duplicates.
  • Each 3x3 block must be filled in with numbers 1 to 9 without duplicates.
  • Each game starts with cells already filled in to help players find the unique solution.
  • The game is completed once a player fills in all cells with the correct numbers.

Example of a completed Sudoku Board

Beginner Sudoku Strategies: Everything you Need to Know to Solve Sudoku Challenges

Last Free Cell

The last free cell is considered a beginner’s solving strategy which will help you complete Sudoku puzzles with many other cells that are already filled in. This strategy uses the logic from the following rules:

  • Each 3x3 block (nonet or subgrid) can only contain numbers 1 to 9 once.
  • Each column can only contain numbers 1 to 9 once.
  • Each row can only contain numbers 1 to 9 once.

Once the Sudoku puzzle is at the point where all eight cells have been filled in a 3x3 block, vertical column, or horizontal row – the last remaining cell will be the number from 1 to 9 which is missing.

Last Remaining Cell

The last remaining cell follows the rules that a 3x3 block (nonet), vertical column and horizontal row should not have the number 1 to 9 repeated in them. This strategy involves looking at the intersection of the three at the same time finding any instances where there is only one free cell left to place a block.

Last Possible Number

The last possible number is a simple strategy to help you find the missing number within a cell. You must look at the numbers that already exist in the 3x3 block, vertical column and horizontal row that are connected to the cell you are trying to find. Keep track of the digits used from 1 to 9 within all the connected blocks to the free cell. The process of elimination can be used to find which value has not been used.

Notes in Sudoku

Notes are a great strategy to use when you are stuck on finding a solution but are unable to see any obvious answers. Notes can be filled into free cells which helps highlight their potential values compared to the other surrounding cells. Many beginner, intermediate and advanced strategies use the notes within free cells to help solve the puzzles.

Obvious Singles

The strategy of obvious singles, which is also known as naked singles, is based on the correct placement of notes. For this strategy, start by filling in notes for the potential numbers 1 to 9 that a free cell could potentially contain. While most of the free cells will have multiple notes, it is the instances where there is only one note in the cell, that it is considered an obvious single. These cells can have their value filled in as there is only one possible solution.

Obvious Pairs

Obvious Pairs is another strategy that Is based on the correct placement of notes within the grid. For this strategy, you need to look for notes within a 3x3 block that contain the same pair of notes. Since these two cells only have these two options, these numbers can be deleted from the other cells within the 3x3 block. This will help reduce the notes for other free cells within the 3x3 block uncovering the ability to apply other strategies such as Obvious Singles.

Obvious Triples

For this strategy to work correctly, notes need to be filled correctly in the grid. This strategy starts with looking at the notes within a 3x3 block. If there are three cells that contain two notes each, with only three values from 1 to 9 being used, these values can be removed from the notes of the other free cells within the 3x3 block.

Hidden Singles

Hidden Singles is a simple technique that can be used to quickly fill in a free cell – it must be noted that this is like the Obvious Singles technique apart from being slightly more difficult to find. This strategy requires that notes are correctly filled in. If a row, column, or block contains only one cell that has a value 1 to 9 as a note – that number should be used to complete the cell. What makes this strategy more difficult from Obvious Singles, is the fact that the note for the free cell will be crowded with other potential values. It is only when looking at the note in context of the row, column, or block where it will stand out.

Hidden Pairs

The Hidden Pairs technique requires that you fill in the notes correctly. For this strategy, within a 3x3 block for cells that contain the same pair of notes. This can prove to be difficult since the notes will be crowded with other values, in essence hiding the two pairs. Once the pair has been identified, this strategy works like the Obvious Pairs strategy where these numbers can be deleted from the other cells within the 3x3 block.

Hidden Triples

Hidden Triples has you compare the notes within a 3x3 block to find three free cells that contain the same three numbers. This can prove to be challenging at first since other notes will be filled into these cells hiding the three numbers. Once three cells are found with the same three values in each, the other notes can be removed from the free cells. This strategy reduces the notes in a 3x3 block which will help reduce complexity to solve the puzzle.