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My 1st Backtrack solution in Clear category for Sudoku Solver by dig
def checkio(board):
def find_first_zero():
for i in range(9):
for j in range(9):
if board[i][j] == 0:
return (i, j)
return None
def is_valid(row, col, num):
for i in range(9):
if board[row][i] == num or board[i][col] == num:
return False
box_row = (row // 3) * 3
box_col = (col // 3) * 3
for i in range(box_row, box_row+3):
for j in range(box_col, box_col+3):
if board[i][j] == num:
return False
return True
def backtrack():
zero = find_first_zero()
if zero is None:
return True
else:
row, col = zero
for num in range(1,10):
if is_valid(row, col, num):
board[row][col] = num
if backtrack() != False: #it no goes after the "!=" except last number is occuped
return True
else: #this case is when line 40 in the recursion is executed
board[row][col] = 0
return False
backtrack()
return board
if __name__ == '__main__':
#These "asserts" using only for self-checking and not necessary for auto-testing
assert checkio([[0, 7, 1, 6, 8, 4, 0, 0, 0],
[0, 4, 9, 7, 0, 0, 0, 0, 0],
[5, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 8, 0, 0, 0, 0, 5, 0, 4],
[0, 0, 0, 3, 0, 7, 0, 0, 0],
[2, 0, 3, 0, 0, 0, 0, 9, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 9],
[0, 0, 0, 0, 0, 3, 7, 2, 0],
[0, 0, 0, 4, 9, 8, 6, 1, 0]]) == [[3, 7, 1, 6, 8, 4, 9, 5, 2],
[8, 4, 9, 7, 2, 5, 3, 6, 1],
[5, 6, 2, 9, 3, 1, 4, 7, 8],
[6, 8, 7, 2, 1, 9, 5, 3, 4],
[9, 1, 4, 3, 5, 7, 2, 8, 6],
[2, 5, 3, 8, 4, 6, 1, 9, 7],
[1, 3, 6, 5, 7, 2, 8, 4, 9],
[4, 9, 8, 1, 6, 3, 7, 2, 5],
[7, 2, 5, 4, 9, 8, 6, 1, 3]], "first"
assert checkio([[5, 0, 0, 7, 1, 9, 0, 0, 4],
[0, 0, 1, 0, 3, 0, 5, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 8, 5, 9, 7, 2, 6, 4, 0],
[0, 0, 0, 6, 0, 1, 0, 0, 0],
[0, 2, 6, 3, 8, 5, 9, 1, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 3, 0, 5, 0, 2, 0, 0],
[8, 0, 0, 4, 9, 7, 0, 0, 6]]) == [[5, 6, 8, 7, 1, 9, 3, 2, 4],
[9, 7, 1, 2, 3, 4, 5, 6, 8],
[2, 3, 4, 5, 6, 8, 7, 9, 1],
[1, 8, 5, 9, 7, 2, 6, 4, 3],
[3, 9, 7, 6, 4, 1, 8, 5, 2],
[4, 2, 6, 3, 8, 5, 9, 1, 7],
[6, 1, 9, 8, 2, 3, 4, 7, 5],
[7, 4, 3, 1, 5, 6, 2, 8, 9],
[8, 5, 2, 4, 9, 7, 1, 3, 6]], "second"
print('Local tests done')
April 16, 2023
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