Your IQ

Sudoku is a captivating logic puzzle that has taken the world by storm. Despite using numbers, it requires no mathematical skill—only pure logic and deduction. The goal is to fill a 9x9 grid so that each column, each row, and each of the nine 3x3 subgrids (also called "boxes" or "regions") contain all of the digits from 1 to 9. This guide will walk you through the fundamental rules and introduce the core techniques that will allow you to solve Sudoku puzzles systematically.

The Three Core Rules

The entire puzzle is governed by three simple constraints:

1. Each row must contain the numbers 1 through 9, without repetition.
2. Each column must contain the numbers 1 through 9, without repetition.
3. Each 3x3 box must contain the numbers 1 through 9, without repetition.

Every step you take in solving a Sudoku must obey all three of these rules simultaneously.

Beginner Technique 1: Scanning (Cross-Hatching)

This is the most basic and essential technique. It involves scanning the rows and columns to find where a specific number can or cannot go in a given box.

How it works:

1. Pick a number to focus on (let's say, the number 5).
2. Pick a 3x3 box to analyze.
3. Look at the three rows that intersect this box. If any of these rows already contains a 5, you know that the 5 in your chosen box cannot be in that row.
4. Look at the three columns that intersect this box. If any of these columns already contains a 5, you know that the 5 in your chosen box cannot be in that column.
5. By "cross-hatching" or eliminating the rows and columns where the number already exists, you can often isolate the one and only cell within the box where the number can legally go.

You should systematically go through all numbers from 1 to 9, applying this scanning technique to every box. This alone can solve most easy-level puzzles.

Beginner Technique 2: Elimination (Finding Naked Singles)

This technique is the flip side of scanning. Instead of focusing on a number, you focus on an empty cell.

How it works:

1. Choose a single empty cell.
2. Look at its row and identify all the numbers that are already in that row.
3. Look at its column and identify all the numbers that are already in that column.
4. Look at its 3x3 box and identify all the numbers that are already in that box.
5. By listing all the numbers from 1 to 9 and crossing out all the numbers you found in its row, column, and box, you can see which numbers are "possible" for that cell.
6. If only one number is left, you have found a "Naked Single." This is the only number that can possibly go in that cell, so you can fill it in with confidence.

Pencil Marks: Your Key to Harder Puzzles

When you can no longer find any numbers using scanning or elimination, it's time to use "pencil marks." This involves writing the possible candidates for each empty cell in small numbers inside the cell. For example, if a cell could be a 2, 6, or 9, you would write a tiny "269" in it.

Once you'vefilled in the pencil marks, you can start using more advanced techniques (like finding "Hidden Singles," "Pairs," "Triples," etc.) that rely on analyzing the patterns in these candidate numbers. But even just the act of writing them down can often help you spot a Naked Single you missed before.

Sudoku is a game of patience and methodical deduction. Don't guess. Every number you place should have a logical reason behind it. By applying these fundamental techniques, you'll find the deep satisfaction that comes from bringing order to the grid, one number at a time.