# Sudoku - medium

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**Sudoku - online**

When you fill a square with the correct digit, the number will turn green, but at a certain point of the game it is possible that more digits could be correct. If at that certain point the digit is incorrect, it will turn red. It is possible that after filling the other squares, some of the digits written down previously won’t be correct anymore. In this case the number won’t change its color, you’ll have to find the incorrect digit in the grid.

The goal of this online Sudoku game available for free on this site is to fill the 9×9 grid with digits from 1 to 9 in such a way that every number can appear only once in each row and in each column, but they must appear at least once. The smaller subgrids containing 9 squares also must be completed in such a way that they only contain each digit once. In the menu you can choose from 4 different levels of difficulty: easy, medium, difficult or extremely difficult. You can also opt for a 4x4 board as well. If the digit you want to fill a square with is definitely wrong at that moment (because it is already in the subgrid or in the given row or column), the number will turn red. Otherwise, the number will turn green. It is possible that, because of the digits you enter later, the given solution won’t be correct anymore, but the number won’t change its color to red. In this case, you’ll have to find the incorrect digit in the grid.If you select the easiest level, there are already 24-25 digits in the grid when you start the game. In round figures it means 30% of the grid.