Beginner Sudoku Guide

The Basic Rules of Sudoku

Sudoku is a puzzle of pure logic. There is absolutely no math or guesswork required. The game is played on a 9x9 grid, which is divided into nine 3x3 sub-grids (called boxes).

To win the game, you must fill all 81 squares on the grid with numbers from 1 to 9, adhering to three golden rules:

1. The Row Rule: Every horizontal row must contain all numbers from 1 to 9 exactly once.
2. The Column Rule: Every vertical column must contain all numbers from 1 to 9 exactly once.
3. The Box Rule: Every 3x3 box must contain all numbers from 1 to 9 exactly once.

Your First Strategy: Cross-Hatching

When you start an "Easy" puzzle, there will be many numbers already filled in for you (called givens). Your goal is to use these givens to logically deduce where other numbers must go.

Cross-Hatching is the easiest way to do this:

• Pick a number (let's say, 5).
• Look at the top three 3x3 boxes. If the left box has a 5 in the top row, and the middle box has a 5 in the bottom row, that means the right box CANNOT have a 5 in the top or bottom row.
• Therefore, the 5 for the right box MUST go somewhere in its middle row. If there is only one empty space in that middle row, you have found your answer!

Counting (Naked Singles)

The second fundamental technique is simply counting what is missing. Sometimes a cell is so surrounded by other numbers that it can only possibly be one digit.

If you look at an empty cell, and you see a 1, 2, 4, 5 in its row... a 6, 7, 8 in its column... and a 9 in its 3x3 box, the only number left in the universe that can fit in that cell is a 3. You can safely lock it in.

The Golden Rule: Never Guess

As a beginner, you will often find yourself stuck. It is incredibly tempting to pick a cell that "looks like a 7" and put a 7 there just to keep the game moving. Do not do this.

If you guess incorrectly, you will build the rest of the puzzle on a false foundation. You won't realize your mistake until 10 minutes later when you end up with two 8s in the same row, and the entire board is unrecoverable.