To find the minimum number of islands for a given set of cloud cover,
you want to assume every island is as large as possible (and thus
includes as many known 'I's as possible) without introducing
unnecessary islands.

For instance,

   ICCI

should be a single island, but

   WCCW

should be zero islands.

The simplest way to do this is to flood-fill from every seen 'I',
traversing both 'I' and 'C' values, setting all to 'W'.  The number
of flood-fills you need to do is the number of islands.

The small data size allows the use of a simple recursive flood-fill.