In this video, I'm just going to go 
through some of the basic terminology and 
rules of Sudoku. 
So this is really kind of like a domain 
analysis for the problem we're about to 
solve. 
So first, Sudoku is played on a nine by 
nine board. 
because it's nine by nine, the board has 
81 of what we're going to call squares. 
In addition to the 81 squares, we say 
that the board has 9 rows, because it's a 
nine by nine board, nine columns. 
Cause it's a nine by nine board, and it 
also has nine boxes, where the boxes are 
little three by three blocks of the whole 
board. 
And so there's three boxes at the top, 
three boxes kind of in the middle and 
three boxes at the bottom. 
So, the rows, the columns and the boxes 
together, comprised what are called 
units. 
There's 27 total units, because there's 
nine rows, nine columns, and nine boxes. 
And adding nine, nine and nine gets 27. 
So there's 27 total units and now we have 
enough terminology to concisely say the 
goal of the game. 
The goal of the game is to fill every 
square with a natural number from one to 
nine, but making sure there's not a 
duplicate number in any unit. 
So there can't be a single row that has a 
duplicate number in it. 
There can't be a single column that has a 
duplicate number in it. 
And there can't be a single box that has 
a duplicate number in it. 
Because we have the term unit we can say 
that more concisely as there can't be a 
single unit that has a duplicate number 
in it. 
So just to be clear, this is an illegal 
move. 
You can't put a six in that third box in 
the first row, because there's already a 
six in that row. 
So that's an illegal move. 
Here's another illegal move, you can't 
put a one there because there's already a 
one in that column. 
So that's an illegal move. 
And here's another illegal move. 
You can't put a three there, you can't 
put the red three in because there's 
already a three in that box. 
That's an illegal move. 
Again, the goal of the game is to fill in 
every square. 
Was a natural from one to nine inclusive, 
but making sure that there's not a 
duplicate number in any unit. 
So that's the quick terminology of Sudoku 
and a quick summary of the rules. 
Again, if you've never seen Sudoku before 
and you'd like a bit more detailed 
introduction to the rules of the game. 
Just do a web search and find one of the 
many Sudoku sites, and you can play one 
or two quick games before picking up the 
next video.