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.

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


def check_sudoku(p):
  n = len(p) # Extract the size of grid
  digit = 1 # Start with 1
  while digit <= n: # Go through each digit
    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 i'th row/column
        if p[i][j] == digit: # check row count
          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 # next row / column
    digit = digit + 1
  return True # Nothing was wrong




print check_sudoku(incorrect)
#>>> False