text: board = [
      [7, 8, 0, 4, 0, 0, 1, 2, 0],
      [6, 0, 0, 0, 7, 5, 0, 0, 9],
      [0, 0, 0, 6, 0, 1, 0, 7, 8],
      [0, 0, 7, 0, 4, 0, 2, 6, 0],
      [0, 0, 1, 0, 5, 0, 9, 3, 0],
      [9, 0, 4, 0, 6, 0, 0, 0, 5],
      [0, 7, 0, 3, 0, 0, 0, 1, 2],
      [1, 2, 0, 0, 0, 7, 4, 0, 0],
      [0, 4, 9, 2, 0, 6, 0, 0, 7]
  ]
  
  # print(len(board))
  
  
  def print_board(bo):
  
      for i in range(len(bo)):
          if i % 3 == 0 and i != 0:
              print("-----------------------")
  
          for j in range(len(bo[0])):
              if j % 3 == 0 and j != 0:
                  print(" | ", end="")
  
              if j == 8:
                  print(bo[i][j])
              else:
                  print(str(bo[i][j]) + " ", end="")
  
  
  print_board(board)
  
  
  def find_empty(bo):
  
      for i in range(len(bo)):
          for j in range(len(bo[0])):
              if bo[i][j] == 0:
                  return (i, j)  # row ,column
      return None
  
  
  def valid(bo, num, pos):
      '''
      Check the row and column and the 3*3 box
      '''
      for i in range(len(bo[0])):
  
          if bo[pos[0]][i] == num and pos[1] != i:
              return False
  
      for i in range(len(bo)):
          if bo[i][pos[1]] == num and pos[0] != i:
              return False
  
      # for box
  
      box_x = pos[1] // 3
      box_y = pos[0] // 3
  
      for i in range(box_y * 3, box_y * 3 + 3):
          for j in range(box_x * 3, box_x * 3 + 3):
              if bo[i][j] == num and (i, j) != pos:
                  return False
      return True
  
  
  def solve(bo):
  
      find = find_empty(bo)
      if not find:
          return True
      else:
          row, col = find
  
      for i in range(1, 10):
          if valid(bo, i, (row, col)):
              bo[row][col] = i
  
              if solve(bo):
                  return True
  
              bo[row][col] = 0
  
      return False
  
  
  solve(board)
  print("\n")
  print_board(board)
  