Sudoku & Kakuro Logic Rules

[TikiPrincess 0]

My in-laws and I have a little tradition of gathering around the kitchen table and trying to finish the crossword puzzle in the daily paper. Usually we could finish up Wednesday's, but Thursday and on got to be much harder and we all had to put our heads together to figure it out. A couple years ago, a new section in the local paper appeared next to the crossword puzzle. A nine-by-nine square with a bunch of numbers in it called SUDOKU.

At first, I was a little wary of it because it just looked a little confusing and intimidating. Basically, you have to fill in the missing numbers. Each row and column must contain the numbers 1 through 9. Additionally, each 3 x 3 section of the puzzle must also have 1 through 9. How do you even begin to solve something like that? Well, there are many different methods, but only one solution.

Let's start in the 3 x 3 section in the bottom-right corner.

There are four empty squares in this section at the bottom-right corner of the puzzle. There's a 2, an 8 and an empty square on the top row, and we're missing numbers 1, 3, 4 and 6.

We can't plug the 1 into the top row of the section because there's already a 1 in the column. We also can't put it in any of the squares on the second row of the section because there's already a 1 in that row. Therefore, the 1 has to be in the empty square at the bottom, and we only have three empty squares now!

The 3 is a little harder. We know that it can't be in the empty square in the top row because there's already a 3 in that column. This means it could be either of the two squares in the second row. You can pencil in 3 in each of the two boxes or make some sort of mark to remember that it could be there. We'll come back to that later.

Next we tackle the 4. If you look at the second row, neither of them can be a 4 because there's already a 4 in that row. So the 4 must be in the top row!

We've still got the 3 and the 6 to fill in the two remaining squares. Looking at the rows won't help us this time, we've got to look at the columns. The column for the second empty square contains a 6, so we can't put it there. That means that it must be in the first empty square, which leaves a 3 in the second one.

And we've completed the section! It should now look something like this:

Of course, there are different levels of difficulty and this method won't always work. But it's a start!

 

Now onto what some people call "Sudoku's evil older brother" - KAKURO!

Though Kakuro is a much more direct translation of crosswords into numbers, it shares a few rules with Sudoku. The numbers may only be 1 through 9 and cannot appear more than once in the same line horizontally or vertically. However, you have to plug in numbers that add up (or multiply depending on your puzzle) to the number at the top or to the left of the section.

The square with the 7\8 in the center separates the sections, so numbers can repeat below that even if they appear above it and numbers can appear to the right even if they're on the left.

So let's start at the top-left corner.

There's 16, 17 and 35 going across. Since you can only use numbers 1 through 9 in your solutions, 16 and 17 only have one solution each that will fit into the two boxes allotted to them. 16=7+9 and 17=8+9. But we can't really be sure where to put these entries until we look at how they relate to the equations going down.

There's 23 and 30 going down. 23 over three spaces equals 9+8+6. Since 6 can't be the solution to 16 because that would result in the next square being 10, and it doesn't work in 17 either for the same reason, then it must be in the third square. 8 isn't part of the solution for 16, but it does fit into the 17. This leaves 9 in the top square. So you would have 9, 8 and 6 vertically in the first column.

Now we can try to fill in some of the other numbers. 16=9+7 and 17=8+9.

Since we've got two of the four boxes filled for 30-down, why not try to solve for it? If we subtract 9 and 8 from 30, we're left with 13. We can't use 9+4 or 8+5 to solve, because there's already a 9 and 8 in the solution. So we have to use 7+6. But which one should go in which box?

We could look at the 35-across. There's already a 6 in that row, so we can't use the 6 again. So the 7 has to go in that third box and the 6 in the fourth.

And the first section is done! Now fill in whatever else you can. Remember to look for ones where the solution is limited to 2 or 3 options.

I hope you have as much fun exercising your brain with these puzzles as I do! GOOD LUCK AND HAVE FUN!
Edited September 23, 2007 by TikiPrincess (see edit history)

[bishoujo 0]

This is a nicely written tutorial for those who don't know how to play Sudoku. I've never heard of Kakuro before but I might follow your tutorial and try it one day. I am currently hooked on Sudoku and I do one everyday. It is mentally stimulating.

[angad619 0]

Nice tutI was addicted to Sudoku till some time ago. But then it seemed t become passe with experience. But then I saw Kakuro and got hooked onto it. It really is the evil older brother. Sure makes my early mornin visit to loo much more interesting.The bigger the puzzle, the more interesting it gets.There've been a few variations too. Yesterday I saw a sudoku with 16x16 squares with numbers from 1-9 and A-F. Can get a bit more time comsuming but as simple nevertheless.But who started Sudoku still remains a mystery. The Indians say an Indian invented it. The Japanese say they invented it!!!

Edited September 25, 2007 by angad619 (see edit history)

[master_bacarra 0]

my younger brother just recently introduced me to kakuro. personally i think it's a lot easier than sudoku. i still think sudoku is better, and the killer sudoku even better. i remember when those two stuff were introduced to me, i wasn't taking it seriously because my mind was totally blank. i could answer some stuff but my mind was wandering somewhere else.

[Galahad 0]

I\ve heard of Sudoku, a while back... However, I was reluctant to try and solve it, because it had numbers in it! And I really, and I mean REALLY, don't like anything remotely related to mathematics (yeah, I know, a programmer that hates math, but yeah, we do exist )... Anyways, a few weeks back, I decided to try Sudoku, don't know why... So I found an online version (one player), and gave it a try... At first, I couldn't get it - how the hell can one guess where the numbers were... So, my first Sudoku game lasted about 50 minutes... Then, as I practiced, I started developing some strange strategy, looking at 3x3 squares, rows, columns, trying to determine which number goes where... And now, I'm hooked... I must play Sudoku, at least once a day, or I go nuts...

 

Of Kakuro I heard, but never saw it, and now that I know how it looks like, and what it requires, I can with certainty say - there is no way in hell I'll be playing this! Yeah, you guessed, too much math

 

Sadly, no newspapers in my country, or at least those that I can get a hold of, don't print Sudoku, just old plain boring crosswords... Maybe I'll start a Sudoku Mag or something...

 

Anyways, great tutorial, wish you wrote it when I started playing, then I wouldn't need 50 minutes to solve my first Sudoku

[hippiman 0]

I saw Sodoku a while ago(probably a couple of years), and I've seen my friends trying to do it, but it wasn't very challenging, so I got bored after like the first 2. I might try the kakuro, though, if I can find one.

[Sprnknwn 0]

Nice tutorial, I think you explain very well what are these two games. Sudoku have become really popular, I don't know if its a global phenomenon but here in Spain we didn't know sudokus like 3 years ago and now they're in every newspaper and lots of people do them going to school, work, etc. It's kind of a fever indeed. Those kakuros aren't so popular or at least I didn't know them... but who knows, maybe they're the next fashion in newspaper games. And now kids make sudokus in their nintendo ds and that so it's really extended.For me both are too... I wouldn't say difficult but I don't get any joy by completing a sudoku, so I don't waste my time trying it (or at least trying it hard). I prefer old fashioned crosswords.

[pop 0]

i need translate this tutorial for my mother. she play sudoku, but can not complete game sometime. she needs book and similar about sudoku, and i need go to library to find book for my mother

[Joshua 0]

Some other tactics I'd mention for Sudoku involve the fact that all #'s 1-9 must exist in a row, a column, and a section. So one easy way to easily improve your Sudoku game is to start looking for rows, columns, or 1 of the 9 sections that have a lot of numbers filled up. Say a row has 6 #'s in it, or a column has 7, or a section of the grid has 5; then you just figure out which numbers are missing in the row/column/section and try seeing which ones can fit in.Also, it's a lot easier if you make little notations of numbers inside the boxes for possibilities that could work in the box. Then you can just erase them and put in the number when you figure out what it is. I don't like that method though because it makes it too easy and removes some of the mental computation needed.

Edited October 15, 2007 by Joshua (see edit history)

[canner2u 0]

I really enjoy Sudoku but have not tried Kakuro ... thank you so much for the tutorial on how to do both of these ... I will have to find where I can play Kakuro online ...Candy