Play Sudoku – The Ultimate Number Puzzle Game
Sudoku is a classic logic-based number puzzle game that challenges players to fill a 9×9 grid with numbers so that every row, column, and 3×3 section contains the digits 1 through 9 without repetition.
I love how Sudoku exercises the brain, improving logic, pattern recognition, and concentration. Whether you’re a beginner learning the basics or an expert solving complex puzzles, Sudoku provides endless mental stimulation and satisfaction.
Sudoku Rules
Every Sudoku puzzle consists of a two-dimensional grid of nine rows and nine columns—essentially a nine-by-nine spreadsheet with 81 spaces, often called “cells.” In addition, the Sudoku grid is divided into nine three-by-three squares (also known as “boxes”), each comprising nine cells. The object is to fill all 81 cells with a number from one through nine, subject to two caveats:
- No number may appear more than once in any “house,” meaning a row, column or square.
- Each game begins with some of the 81 cells already filled in. These “givens” actually provide all the information you need to solve the puzzle. So, the general rule is that the fewer the givens, the more challenging the grid will be.
Sudoku glossary
| Cell | Each of the 81 spaces in a Sudoku puzzle |
| Square | Each of the nine three-by-three xsquares, also known as “boxes” |
| House | Each of the nine rows, columns or squares |
| Given | Cells that have a pre-filled number at the start of the game |
| Candidates | Every number (one through nine) that could be slotted into a particular cell |
| Chutes | Three adjacent vertical or horizontal nine-by-nine squares |
Sudoku puzzles tend to come labeled by their degree of difficulty. Regardless of how easy or hard the puzzle is, all must be solved in the same way, and that is through the process of elimination. “Any blank cell could, in theory, contain any of the digits one to nine,” Anthony and Goodliffe tell Reader’s Digest. Sudoku game-play consists of eliminating wrong numbers until only the right ones remain. What follows is the best way to go about it, according to the guys behind Cracking the Cryptic.
Understand “candidates”
Reader’s Digest
In Sudoku parlance, every digit (one through nine) that could be slotted into a cell on a grid is known as a candidate. But “if a digit already appears elsewhere in a blank cell’s row, column or square, then that digit cannot be a candidate for that particular blank cell,” Anthony and Goodliffe explain. In other words, with regard to any blank cell, if a digit already exists elsewhere in its house, then that digit is not a candidate.
Don’t use “automatic candidates”
Anthony and Goodliffe recommend against resorting to “automatic candidates,” a setting in many on-screen iterations of Sudoku that allows you to make all candidates visible with a single click. As tempting as that may seem, the downside is that “it can be difficult to see even simple patterns within the Sudoku grid when every cell has lots and lots of markings in it.”
Don’t guess
There are many worthy Sudoku strategies to help you fill out the grid, but guessing is not one of them. As Anthony and Goodliffe put it, “Guessing avoids finding the logic that most Sudoku puzzles inherently possess and therefore you neither maximize your chance of finding the solution nor improve your skills.” Indeed, a legitimate or “fair” Sudoku grid should require no guessing at all, and our experts advise steering clear of any that do. Fortunately, those that you’ll find in newspapers and magazines, and many you’ll find online, tend to be fair, our experts tell us.
Most Sudoku grids will come with some number of blank cells for which, thanks to the placement of givens, only one candidate is possible. Of course, the harder the puzzle, the fewer of these you will find. However, if they’re there, it’s by design, and a good scan of a fresh grid should reveal them. Because every cell you fill in offers new information about the remaining empty cells, Anthony and Goodliffe recommend starting your Sudoku-solving by seeking out this “low-hanging fruit” in the rows, columns and squares that contain the greatest number of givens.
Take the “square route”
Perhaps the most popular Sudoku strategy is to focus specifically on what Anthony and Goodliffe refer to as “chutes” of three adjacent nine-by-nine squares. These occur both vertically and horizontally. The rule of thumb, which some people refer to as the “three number rule” is that “a digit must appear three times per chute but only once per row, column and box.” So, begin by scanning for rows or columns within the chute that already have two of the same digit. This will hone it down to a single row or column where the third occurrence of that digit fits.
Often, there will only be one particular cell where the third instance of that digit can go; if so, you’re now one step closer to solving the puzzle overall. Other times, however, there may be two or three cells where a digit could go. And this is where this next Sudoku strategy comes in.
Reader’s Digest
Once you have identified a number that can fit into two or even three possible cells in one house, it’s time to break out the “pencil-marking” strategy, which Anthony and Goodliffe tell us was first popularized by three-time World Sudoku Champion Thomas Snyder.
The way it works is that “if there’s one digit that can go in exactly two cells in one square, you put a little “pencil mark” (or otherwise note the digit is a candidate) in the corner of each of those two cells.” As you fill in more cells, it should eventually become obvious which of these cells is the correct one for that digit. (Although it probably goes without saying, when playing Sudoku online, you won’t need an actual pencil; most online iterations of the game allow you to work in pencil-marking mode, although they may call it something else such as “Notes” or “Candidates” mode.)
Find and make use of Hidden Pairs and Hidden Triples
Reader’s Digest
The pencil-marking strategy is so effective, according to Anthony and Goodliffe that once you master it, you’ll be able to solve virtually any Sudoku puzzle—even the most difficult. Even better, pencil marking will help you finish faster. That’s because once you’ve mastered pencil marking, you can move on to the important Sudoku strategies known as Hidden Pairs and Hidden Triples.
A Hidden Pair refers to two candidates that appear in two cells in the same house and nowhere else in the house (remember, a house is any of a single row, column or square) where at least one of the two cells has other candidates. Those other candidates can be summarily eliminated—without another thought. But if you do want to think about it, the reason is that of those two candidates, one is the solution to one of those two cells, and the other candidate is the solution for the other cell. Therefore, the unpaired candidates in those two cells cannot possibly be the solution to either.
Using Hidden Triples works the same way except that there have to be three cells in which the same three candidates appear, and those same three candidates cannot appear in any other cell.
Practice and practice some more
If you’re a beginning Sudoku player looking to improve your game, there’s no substitute for practice, say Anthony and Goodliffe. Not only will you get better at recognizing patterns within your pencil markings, but you’ll also be better equipped to use some of the more advanced Sudoku tips and tricks. Of these, “X-Wing” is arguably the simplest, although there’s really nothing simple about it.
X-Wing refers to a scenario in which one candidate occurs in two cells in each of two rows, and those two cells are also located in the same two columns. As long as there are no other cells for which the digit in question is a candidate, you’ll be able to eliminate all other candidates in all four of the cells. And that, of course, can be very useful.
Source: rd.com/article/sudoku-tips/©
