S - Sudoku

Sudoku is a number placement puzzle. The objective is to fill a 9×9 grid with digits so that 1) each column, 2) each row, and 3) each of the nine 3×3 sub-grids contains all of the digits from 1 to 9 only once. You start with a partially filled grid, which you have to complete. Each puzzle has a unique solution. It is a fun puzzle and I like doing it a lot. Since it comes in the newspapers, I have been solving one puzzle each day for quite some time now. (I also like doing the ‘Loop the Loop’ & ‘Hitori’ puzzles which come in TOI) Math has always been my favourite subject so I am interested in anything that has to do with numbers. At the cost of sounding vain, one of the things that even my seniors at work appreciate is my comfort with financial numbers. In my appraisals, this has been mentioned as one of my strengths  for years now! :-D

Any ways, enough of blowing my trumpet.. ;-), I digressed. First time when I played Sudoku was back in 2006. I was in Bangalore and this puzzle started coming in the newspapers. There was an interesting co-incidence related to it at that time. I had travelled to US for a job assignment in 2006. During Christmas, we had a party at my director’s house. One of the games that they had planned was a game of Sudoku. We were given the puzzles and the person who finished it first would be the winner. As I had done it in the past and was really fast at it, I was the first one to complete it. In fact, I completed it in less than 3 minutes. Most of the people from my client side as well as team were very impressed. I got a nice gift coupon for Barnes and Noble (a book store there) as prize!

Here is how I go about solving it:

- I try to begin by looking at the 3X3 sub-grids which are the most populated. Based on the numbers present, I decide which of the 1-9 are missing and should be there.

- Then I start looking at the corresponding row and column to see the missing number can fit in there. Many a times, some numbers get rejected and only 2-3 choices remain. Sometimes you get even the one confirmed number with this elimination technique.

- Then I see which number is present the most times as each should be present 9 times in the entire puzzle. I pick that number and start checking that it’s present in each 3X3 sub-grid. If not, I try placing that number in the missing sub grid using the elimination technique again.

- Once you start filling in the numbers, it also helps in solving for other numbers which had 2-3 placement options before.

- Solving this way, you sometimes reach a point where you are stuck with 2-3 numbers looking equally right for a particular cell. If this is the case, move back and check everything again. You would have missed out on one number, getting it right will make others fall into place and complete the puzzle for you.

- If sometimes, I am not sure of what to put in a cell, I make a note of all the possible numbers that can fit in there and look at the overall puzzle again. It helps.

- There are some Sudoku’s which are really hard and take time but they can be solved. Always!