input: Write a function to solve any Sudoku puzzle. The function should take a 9x9 grid as input where blank cells are represented by the digit 0 and should print the solved puzzle if a solution exists or print "No solution" otherwise.
  assert solve_sudoku([
      [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]
  ])==[
      [7, 8, 5, 4, 3, 9, 1, 2, 6],
      [6, 1, 2, 8, 7, 5, 3, 4, 9],
      [4, 9, 3, 6, 2, 1, 5, 7, 8],
      [8, 5, 7, 9, 4, 3, 2, 6, 1],
      [2, 6, 1, 7, 5, 8, 9, 3, 4],
      [9, 3, 4, 1, 6, 2, 7, 8, 5],
      [5, 7, 8, 3, 9, 4, 6, 1, 2],
      [1, 2, 6, 5, 8, 7, 4, 9, 3],
      [3, 4, 9, 2, 1, 6, 8, 5, 7]
  ]
  assert solve_sudoku([
      [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],
      [0,0,1,9,False,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]
  ])==False
  assert solve_sudoku([])==False
output: def solve_sudoku(grid):
      def is_valid(grid, row, col, num):
          for x in range(9):
              if grid[row][x] == num:
                  return False
              if grid[x][col] == num:
                  return False
              if grid[row//3 * 3 + x//3][col//3 * 3 + x%3] == num:
                  return False
          return True
  
      def solve():
          for row in range(9):
              for col in range(9):
                  if grid[row][col] == 0:
                      for num in range(1, 10):
                          if is_valid(grid, row, col, num):
                              grid[row][col] = num
                              if solve():
                                  return True
                              grid[row][col] = 0
                      return False
          return True
  
      if not all(isinstance(row, list) and len(row) == 9 for row in grid):
          return False
      if len(grid) != 9:
          return False
  
      if solve():
          return grid
      else:
          return "No solution"