Text based Sudoku Solver

def is_valid(board, row, col, num):

  for i in range(9): # Number repeated in row?

    if board[row][i] == num:

      return False

  

  for i in range(9): # Number repeated in column?

    if board[i][col] == num:

      return False

  

  # Is number repeated in 3x3 subgrid

  start_row, start_col = 3 * (row // 3), 3 * (col // 3)

  for i in range(start_row, start_row + 3):

    for j in range(start_col, start_col + 3):

      if board[i][j] == num:

        return False

  return True

def solve_sudoku(board):

  for row in range(9):

    for col in range(9):

      if board[row][col] == 0:

        for num in range(1, 10):

          if is_valid(board, row, col, num):

            board[row][col] = num

            if solve_sudoku(board):

              return True

            board[row][col] = 0

        return False

  return True

def print_board(board):

  for row in board:

    print(" ".join(str(num) for num in row))

grid = [[5, 3, 0, 0, 7, 0, 0, 0, 0],

        [6, 0, 0, 1, 9, 5, 0, 0, 0],

        [0, 9, 8, 0, 0, 0, 0, 6, 0],

        [8, 0, 0, 0, 6, 0, 0, 0, 3],

        [4, 0, 0, 8, 0, 3, 0, 0, 1],

        [7, 0, 0, 0, 2, 0, 0, 0, 6],

        [0, 6, 0, 0, 0, 0, 2, 8, 0],

        [0, 0, 0, 4, 1, 9, 0, 0, 5],

        [0, 0, 0, 0, 8, 0, 0, 7, 9]

       ]

if solve_sudoku(grid):

  print("Sudoku Solved:")

  print_board(grid)

else:

  print("No solution exists.")