25/06/2020
How to resolve sudoku.
The game aims to fill the white boxes with numbers from 1 to 9, so that in every row, in every column and every square region with bold edges, all the digits from 1 to 9 are present without repetitions. But that's just the rule. To solve the problem it takes logic and inventiveness. Someone has found the foolproof method: fill each box with the numbers 1 to 9 and then delete them as you go. It will be pure a resolutive technique but it is of deadly boredom. On the other hand, there is much software that solves the sudoku, just feed the numbers you noticed to the computer and here is the solution to copy. This is also a proven technique but it is certainly not a nice way to play. Where's the fun? So let's imagine sitting on a deckchair near the sea, it's hot, but there is shade and there is a pleasant breeze coming from the sea. Let's take the pencil, the sudoku sheet.
The rule: never the same number
There is only one rule for playing Sudoku: you must fill the board so that each row, each column, and each box contains the numbers from 1 to 9. The condition is that no row, no column or box have the same twice number.
The advice: use reasoning You can guess even to put the first numbers, but it is much more fun to use reasoning and logic to find the right positions for numbers. Each correctly entered number is a piece of additional information to find the others.
The example: how to start The square shown above we use it as an example to suggest some logical techniques to start playing. Look at the 7 in the vertical series to the left of the three boxes. There is a 7 in the upper pane, a 7 in the lower pane, but there is no 7 in the central one. The 7 in the top box applies to the entire first column, the 7 in the bottom box also applies to the entire second column. So the 7 that we have to put in the central box will not go in the first and second columns, but the third. Within the central pane, the third column already has two boxes filled in and one free. That box (marked in the example with the letter A) is the only one that can contain the 7. This technique is called slicing, slicing. Now let's see the 7 in the series of boxes at the top of the grid. The 7 is in the left pane and there is also in the right one, it is missing in the central pane. The 7 of the box on the right is valid for the whole first row, the 7 of the box on the left is valid for the whole second row of boxes. Using the previous logical technique, we know that in this case the 7 must be inserted in box B or box C. But in the first column of the second box, there is a 7, while there is not in the second. Consequently, the 7 should be placed where the letter C is. Going forward and examining the central squares and always the number 7 we see that it is missing in the box to the right of the middle sequence. According to the same reasoning that has already done previously, it is clear that the 7 goes where we put the letter D.
The tools: pencil, eraser, and patience To play Sudoku you just need a pencil, an eraser to erase any mistakes, and a little patience. Start from the numbers that are most present, do not guess, think about it, insert the number only when you are certain, and remember that for each game the solution is one and only one.
The best sudoku book is here:
https://www.amazon.com/dp/B086PRL7YY