Kevin Tse - 10 months ago 60

Python Question

I want to write some Python code to check that whether a matrix accords with the rule of Sudoku. My code is presented below:

`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(matrix):

n = len(matrix)

# check each row

i, j = 0, 0

while i < n:

checked = []

while j < n:

if matrix[i][j] not in checked:

checked.append(matrix[i][j])

j += 1

if len(checked) < n:

return False

i += 1

# check each column

i, j = 0, 0

while i < n:

checked = []

while j < n:

if matrix[j][i] not in checked:

len(checked)

checked.append(matrix[j][i])

j += 1

if len(checked) < n:

return False

i += 1

return True

# the output should look like this:

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

But here's a weird problem in the if statement. After the two inner while loops, the statement "len(checked)" evaluates to 0 which should not be like that. I don't know what happened.

Answer Source

The problem is you're not initializing `j`

properly for the two inner while loops. Here's your code and the indicated modifications to make it work:

```
def check_sudoku(matrix):
n = len(matrix)
# check each row
# i, j = 0, 0
i = 0
while i < n:
j = 0 # added
checked = []
while j < n:
if matrix[i][j] not in checked:
checked.append(matrix[i][j])
j += 1
if len(checked) < n:
return False
i += 1
# check each column
# i, j = 0, 0
i = 0
while i < n:
j = 0 # added
checked = []
while j < n:
if matrix[j][i] not in checked:
checked.append(matrix[j][i])
j += 1
if len(checked) < n:
return False
i += 1
return True
```