Udacity_sudoku.py

# THREE GOLD STARS

# 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.

correct = [[1, 2, 3],
           [2, 3, 1],
           [3, 1, 2]]

incorrect = [[1, 2, 3, 4],
             [2, 3, 1, 3],
             [3, 1, 2, 3],
             [4, 4, 4, 4]]

incorrect2 = [[1, 2, 3, 4],
              [2, 3, 1, 4],
              [4, 1, 2, 3],
              [3, 4, 1, 2]]

incorrect3 = [[1, 2, 3, 4, 5],
              [2, 3, 1, 5, 6],
              [4, 5, 2, 1, 3],
              [3, 4, 5, 2, 1],
              [5, 6, 4, 3, 2]]

incorrect4 = [['a', 'b', 'c'],
              ['b', 'c', 'a'],
              ['c', 'a', 'b']]

incorrect5 = [[1, 1.5],
              [1.5, 1]]


def check_sudoku(sudoku_grid):
    n = len(sudoku_grid) # extract the size of grid
    digit = 1 # start with checking the digit 1
    while digit <= n: # go through each digit between 1 and n
        i = 0
        while i < n: # go through each row and column
            row_count = 0
            col_count = 0
            j = 0
            while j < n: # for each entry in ith row/column
                if sudoku_grid[i][j] == digit: # check row count
                    row_count += 1
                if sudoku_grid[j][i] == digit:
                        col_count += 1
                j += 1
            if row_count != 1 or col_count != 1:
                return False
            i += 1 # next row/column
        digit += 1
    return True




print check_sudoku(incorrect)


# print check_sudoku(incorrect)
# >>> False

# print check_sudoku(correct)
# >>> True

# print check_sudoku(incorrect2)
# >>> False

# print check_sudoku(incorrect3)
# >>> False

# print check_sudoku(incorrect4)
# >>> False

# print check_sudoku(incorrect5)
# >>> False