An attempt by an Elimination and Decision Tree process

Everything about Sudoku that doesn't fit in one of the other sections

An attempt by an Elimination and Decision Tree process

Postby Guest » Thu May 19, 2005 2:46 pm

Hello everyone,

Solved my first Soduku puzzle on the website today. Felt great.

It was really exciting to read newspaper reports on how, a number game was taking so many people by storm. ( I am a crossword enthusiast so did wonder if crosswords were on their way out!)

I just had to have a go at it.

And contrary to how it's mentioned that one can end up taking quite a few false starts before hitting on the right solution i seemed to get lucky in that i got the soluton after just one false decision.

In each cell i wrote down all the numbers acceptable for that cell by eliminating those already in that column, in that row and in that sub matrix ( 3x3 matrix) which the cell belonged to.

In some cells there were upto six possible numbers and in some just two.
I took a cell with the two options and randomly selected one. Next i struck of the selected number whereever it appeared in the column, the row or sub matrix of that cell.

After the first iteration, i rechecked for any cells now having just one number. If a new cell now had just one number, that number could be knocked off from the row, the column and the sub matrix of that cell.

For the second iteration i once again took a decision on a cell having two options. This time i happened to select the wrong one as in one submatrix two cells ended up with the same number.

I simply went back and selected the other one and had the pleasure of seeing the entire matrix unravel.

By the way is it possible for one puzzle to have more than one solution?

P.s - helps to do the puzzle on a spread sheet.

Postby Animator » Thu May 19, 2005 2:50 pm

Actually, normally it is not required to guess a number...

And a puzzle normally has only 1 solutions... ofcourse it depends on who created the puzzle since some allow multiple solutions... but the ones published on the Times etc have only one unique solution.
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