Sudoku Solver

Make a copy/paste or type directly in cells. Letters (Wordoku/alphadoku) and digits are accepted.

Example: Copy the Sudoku content in the first cell (top left) 97 1 5 5 9 2 18 4 8 7 26 92 3 6 2 9 19 4572 to get:

Software solves the 9x9 sudoku almost like an human and display each step of its progress to understand. If a box or a number has only one possibility then it is validated and the solver displays each of the stages of its progress to understand.

Sometimes the reasoning arrives at a stage where no quick logical deduction allows to deduce the value of a box (several possible values). The solver then analyzes the boxes where there are the fewest possibilities and selects a value that it considers the most probable and continues, if an inconsistency occurs (that the sudoku has no more solution) then it returns to step selection and takes another value. To optimize the chances, the selection is not random, the choice is made on a number which, if it is positioned in the box, will allow the maximum of deduction in the continuation of the sudoku. This method is the fastest for the solver, it may be that sometimes a slower and complex deduction could achieve the same result.

NB: If the program indicates that there is only one possible value, it means that no other value is acceptable in the box (the dCode solver is always right).

dCode calculates all the solutions for the sudoku, not only the first one. To check a homemade sudoku, the solver can confirm that there is only one solution.

The first Sudoku versions are from 1979

A line can consist of $ 9! $ (Factorial of 9) different ways, but the whole sudoku has a number of possibilities much less than $ 9!^9 $, because some permutations can lead to identical grids. The total number of grids would be $ 9! \times 72^2 \times 27 \times 27 \times 704267971 = 6670903752021072936960 $ combinations.

By keeping the sudoku NxN rules that require the N characters to be used on each row and column, then it is impossible to respect them if the sudoku is not square.

Some variants of the square sudoku, however, use non-square inner blocks (see sudoku 6x6, sudoku 7x7 or sudoku 8x8)