Sudoku

Sudoku is one of the world's most popular puzzles. It consists of a 9x9 grid, and the objective is to fill the grid with digits in such a way that each row, each column, and each of the 9 principal 3x3 subsquares contains all of the digits from 1 to 9. The detailed rules can be found, for example, here.

Grid Representation

Initial Puzzle

4 . . |. . . |8 . 5 
. 3 . |. . . |. . . 
. . . |7 . . |. . . 
------+------+------
. 2 . |. . . |. 6 . 
. . . |. 8 . |4 . . 
. . . |. 1 . |. . . 
------+------+------
. . . |6 . 3 |. 7 . 
5 . . |2 . . |. . . 
1 . 4 |. . . |. . . 

Solved Puzzle

4 1 7 |3 6 9 |8 2 5 
6 3 2 |1 5 8 |9 4 7 
9 5 8 |7 2 4 |3 1 6 
------+------+------
8 2 5 |4 3 7 |1 6 9 
7 9 1 |5 8 6 |4 3 2 
3 4 6 |9 1 2 |7 5 8 
------+------+------
2 8 9 |6 4 3 |5 7 1 
5 7 3 |2 9 1 |6 8 4 
1 6 4 |8 7 5 |2 9 3 

About This Code

Give the inputs for the sudoku as:

grid = '4.....8.5.3..........7......2.....6.....8.4......1.......6.3.7.5..2.....1.4......'

Demo

References

This project is based on Peter Norvig's post.

Solving Every Sudoku Puzzle