Write a function that will solve a 9x9 Sudoku puzzle. The function will take one argument consisting of the 2D puzzle array, with the value 0 representing an unknown square.
The Sudokus tested against your function will be "easy" (i.e. determinable; there will be no need to assume and test possibilities on unknowns) and can be solved with a brute-force approach.
For Sudoku rules, see the Wikipedia article.
puzzle = [[5,3,0,0,7,0,0,0,0],
[6,0,0,1,9,5,0,0,0],
[0,9,8,0,0,0,0,6,0],
[8,0,0,0,6,0,0,0,3],
[4,0,0,8,0,3,0,0,1],
[7,0,0,0,2,0,0,0,6],
[0,6,0,0,0,0,2,8,0],
[0,0,0,4,1,9,0,0,5],
[0,0,0,0,8,0,0,7,9]]
sudoku(puzzle)
# Should return
[[5,3,4,6,7,8,9,1,2],
[6,7,2,1,9,5,3,4,8],
[1,9,8,3,4,2,5,6,7],
[8,5,9,7,6,1,4,2,3],
[4,2,6,8,5,3,7,9,1],
[7,1,3,9,2,4,8,5,6],
[9,6,1,5,3,7,2,8,4],
[2,8,7,4,1,9,6,3,5],
[3,4,5,2,8,6,1,7,9]]