#  ###
#  # #
#  # #
######
Invalid, because it contains an inner enclosed compartment!

#  ###
#  # #
#  #
######
Invalid, because there is a stalactite!

#  ###
#  #
#  # #
######
Invalid, because there is a stalagmite!

#  # #
#  # #
#  # #
######
Invalid, because there are three top row edges!

######
#    #
#    #
######
Invalid, because there is a single top edge!

#    #
#
#    #
######
Invalid, because there is a gap at the side!

#    #
#    #
#    #
##  ##
Invalid, because there are two gaps on the bottom row!

#    #
#  # #
#  # #
######
Valid, would fill as:
#~~~~#
#~~#~#
#~~#~#
######

#  ###
#  #
#  #
######
Valid, would fill as:
#~~###
#~~#
#~~#
######

#    #
#  # #
#  # #
#### #
Valid, would fill as:
#    #
#  # #
#  # #
####~#
    ~
    ~
    ~
    ~
    ~
    ~
    ~
    ~
    ~