A look at a hard Sudoku

So I thought it would be useful for people to learn how to do the wonderful and amazing sudoku in newspapers and stuff. Well, okay, so it isn't very useful, but at least you won't get stuck or have to guess any more.

A bit of a background on how I learned: I think one day I just saw this sudoku puzzle and I read the rules which are fiendishly simple. I then proceeded to logically think out where all the numbers should be. After a while, I used several different techniques (they all have names at this point and I even read about these 'advanced' techniques in order to get better not realizing that I was already using these techniques that I had come up with on my own)

Anyway, here's a step by step look at a hard sudoku found on websudoku.com.


So here is the start, it looks pretty normal for a sudoku doesn't it?

So to start off, I like to use what I think is called the 'hammer' method. Basically its looking at a single number and easily eliminating all the squares but one to have that number inside a square. It's just a very simple strategy to get numbers quickly - on the easy puzzles, you can solve the whole puzzle using this method, contrastingly, on the hard puzzles, you can only
get a few before you are stuck.











So here we are now with the hammer method completed (well I didn't really double check, but most of its there). Now that we're stuck, we have to rely on a bit of logic now to help us. As many sudoku puzzlers realize, after a certain point, all the numbers just fall into place and from there its extremely easy. Its about getting there one number at a time though so take it slow.










Now take a look at the circles. We can see from the rows, columns and squares that no 3 can be in any of the circles. So the 3 must be in the last available square in the left middle.













After filling in the 3, we can now take a look at the right middle square where the 6 8 9 2 are all circled. From all the circled numbers, we can see that only one number can go into the middle of the right middle square: 4.














Filling in more numbers (like the 3 in the right top square on top of the 6) helps us out even more. Again, we keep applying the hammer method to help us 'hammer' out more and more numbers. Each time we fill in a new number, we can go back to the hammer method to see if any new numbers are revealed.











If we look at the rectangled box, the row is missing a 1, 6 and 7. Immediately to the left of the 4 though, the 6 and 7 cannot possibly be located there because no number can repeat in the same box, row or column. So the 1 must be beside the 4.













Again more hammering out gives us the 1 in the top right corner. Now, lets take a look at the right top square and the row encased in the rectangle. We know from the square that we are missing a 5 and a 8 so in that row, the 5 and 8 (though we do not know which is which) cannot possibly be anywhere else and thus, we can fill in the 7.









Now because we have filled in so many numbers, the hammering starts to get easier and easier.
















And at this point, we have reached the point where everything now moves forward at a very rapid rate.















And finally you solved that hard one! Now you can do those hard ones in the newspapers.