Sudoku (pronounced soo-DOH-koo) is a numbers puzzle. The word Sudoku comes
from the Japanese su- (number) and doku- (single).
An American working with Dell Puzzles invented it in 1979 and called it Number
Place. It started appearing in Japanese newspapers
as Suji wa dokushin ni kagiru (the numbers must occur only once) in the
1980s and was already a big hit there, its name shortened to Sudoku, when a
retired judge vacationed in Tokyo in 1997, was hooked playing it, and resolved
to spread it in the West.
The puzzle appeared in the Times newspaper in London
in late 2004, where it became a craze, leading to published books, television
game shows, and Sudoku tournaments. The public bought more books on Sudoku than
the latest volume of Harry Potter.
Now, the puzzle appears in over 400 newspapers worldwide, including a
growing number in the United States.
Sudoku aficionados compare the spread of the puzzle to the Rubik’s Cube craze
in the early 1980s.
Sudoku’s Appeal
The central appeal of Sudoku is its simplicity. The puzzle is a nine-by-nine
square grid with nine three-by-three mini grids. The goal is to fill the entire
grid so that every row, column, and mini grid contains the numbers 1 through 9,
each number appearing only once in each row, in each column, and in each
mini-grid.
Some of the boxes in the grid already contain numbers that act as clues,
like a crossword puzzle with some of the letters written in. The puzzle solver
starts with these clues and tries to guess how to arrange the other numbers so
that the number appears only once in the row, column, and mini grid.
Each puzzle has only one solution, and one does not have to be a genius or
good at math to solve it. Solving a Sudoku puzzle meticulously demands logic
and patience. It needs a certain degree of mental concentration and is good for
exercising the memory. All these make solving the puzzle exciting.
Levels of Difficulty
Sudoku puzzle designers claim there are four levels of difficulty some
classify as gentle, moderate, tough, and diabolical. Some newspapers use
different terms.
The level of difficulty does not depend only on how many numbers are given
at the start.
Aside from the given numbers, three things determine the puzzle’s
difficulty: how many squares can be filled up by using the process of
elimination, how many guesses are needed to reach the right solution, and how
many times one has to backtrack to solve the puzzle.
A computer that generates these puzzles also classifies the puzzle’s
difficulty based on these four factors.
As I have experienced, the rating assigned by the computer is sometimes not
reliable. The possible reason is that the computer assumes all possible wrong
guesses before arriving at a final solution. However, after playing the puzzle
several times, I learned that luckily making the right guess the first time
allowed me to quickly solve the puzzle.
Some puzzles with a few given numbers are easy to solve, while others with
as many as twenty-seven given numbers are very difficult.
How to Play Sudoku
Learning to play Sudoku is difficult without an illustration, but with a
good imagination, you can get a general idea. If you want to see how a Sudoku
grid looks like, just click on the link at the end of this article and store
that image before we proceed.
The first thing you see when you look at the puzzle is a large square, the
grid, containing 81 squares. This is like a chessboard with nine squares on top
and nine squares on the side, intersecting to form eighty-one squares. This
grid has nine columns going from left to right and nine rows going from top to
bottom.
For every three squares, four thick lines – two drawn from top to bottom and
two drawn from left to right – form a mini-grid of nine squares each. Each
mini-grid is a three by three square so the grid, the large square, has nine
mini-grids.
An easy Sudoku puzzle may have twenty-nine numbers printed in different
squares and several mini-grids. Using these numbers as starting clues, your
goal is to fill up the remaining squares with numbers.
How do you start?
Picture yourself looking at a Sudoku puzzle for the first time. You see the
grid, the mini-grids, and the numbers.
You can start anywhere, but I prefer to take the upper left mini-grid first.
What I do next is move from the left upper mini-grid to the right lowest
mini-grid, filling up each box in the mini-grid with the possible numbers that
can go into each empty square. You will find out what these numbers are from
what you already see printed on each row, column, and mini-grid.
By a process of elimination, you fill in each square, from top-left to
bottom-right, going from the top row to the bottom row in each mini-grid.
Your big problem is the size of the square as printed in the newspaper. How
do I solve this? I duplicate the puzzle on my PDA, enlarge the image, and work
at it.
It takes around ten minutes to fill up all the boxes, and the process of
elimination begins.
These are the clues to watch for:
Look at each mini-grid. Study
each empty square (without given numbers) filled with the numbers that can
go in that square. If a number appears only once in that mini-grid, this
means that that number should be in that square.
When you identify a number
that belongs in a square by this process of elimination, erase that same
number from the other squares in the mini-grid and from squares where it
appears on the same row and column.
Do this for all the nine
mini-grids.
Next, look at each row and
column and do the same process of elimination. If there is a number that
appears only on that row and on that column, then that number belongs in
that square.
Erase that number from the
other squares in the mini-grid. There is no need for you to erase it from
other columns or rows, since it appeared only once.
Do this for all the nine row
and nine columns.
After doing all these meticulously (it usually takes me twenty minutes or
less to do it), you are left with two or three squares in each mini-grid with
two or three numbers that can possibly fit in.
The End Game
This is where the final stage begins. You need to start making guesses to
arrive at the complete solution.
What I do is look for a mini-grid with two squares not filled in. Usually,
there are two numbers left, both of which are the same, and then work from
there.
Guessing that one number goes into a square means it will not go into any
other square in the mini-grid, row, or column. If you guess it right, the
solution reveals itself.
In some Sudoku puzzles, I reach the final stage with three or four squares
not filled in some mini-grids. This makes the guessing game more tedious but
challenging.
With a bit of practice, a quick glance reveals the solution, and the
fulfillment at cracking another Sudoku puzzle fills you with relief.
By this time, close to an hour had passed and your subway
ride is over. Your mind, refreshed and feeling like a winner, is ready to
tackle less serious matters at the office.