Check_sudoku.py

# Sudoku [http://en.wikipedia.org/wiki/Sudoku]
# is a logic puzzle where a game
# is defined by a partially filled
# 9 x 9 square of digits where each square
# contains one of the digits 1,2,3,4,5,6,7,8,9.
# For this question we will generalize
# and simplify the game.

# Define a procedure, check_sudoku,
# that takes as input a square list
# of lists representing an n x n
# sudoku puzzle solution and returns the boolean
# True if the input is a valid
# sudoku square and returns the boolean False
# otherwise.

# A valid sudoku square satisfies these
# two properties:

#   1. Each column of the square contains
#       each of the whole numbers from 1 to n exactly once.

#   2. Each row of the square contains each
#       of the whole numbers from 1 to n exactly once.

# You may assume the the input is square and contains at
# least one row and column.

def check_sudoku ( p ):
    n = len(p)    # extract size of grid
    digit = 1
    
    while digit <= n: 
        i = 0
        while i < n:
            row_count = 0
            col_count = 0
            j = 0
            while j < n:
                if p[i][j] == digit:
                    row_count = row_count + 1
                if p[j][i] == digit:
                    col_count = col_count + 1
                j = j + 1
            if ((row_count ! = 1) or (col_count != 1)) :
                return False
            i = i + 1
        digit = digit +1
    return True