Coded Nurikabe (517)

Shade some cells black (leaving the other cells white) so that the grid is divided into non-overlapping regions; cells of the same color are considered in the same region if they are adjacent horizontally or vertically. Each given number must be in a white region that has the same area in cells as that number. Each white region must have exactly one given number. All black cells must be in the same region. No 2×2 group of cells can be entirely shaded black.
The numbers have been replaced with letters. The same numbers have been replaced with the same letters. Different numbers have been replaced with different letters.

Reference: WPC 2016 (65)