Create ps3-2.suduko.solver.py

# CHALLENGE PROBLEM: 
#
# Use your check_sudoku function as the basis for solve_sudoku(): a
# function that takes a partially-completed Sudoku grid and replaces
# each 0 cell with an integer in the range 1..9 in such a way that the
# final grid is valid.
#
# There are many ways to cleverly solve a partially-completed Sudoku
# puzzle, but a brute-force recursive solution with backtracking is a
# perfectly good option. The solver should return None for broken
# input, False for inputs that have no valid solutions, and a valid
# 9x9 Sudoku grid containing no 0 elements otherwise. In general, a
# partially-completed Sudoku grid does not have a unique solution. You
# should just return some member of the set of solutions.
#
# A solve_sudoku() in this style can be implemented in about 16 lines
# without making any particular effort to write concise code.