Speed up Hobiwan's Fishes

[KyouyamaKazusa0805]

Hobiwan's fish is an extremely and main sudoku technique, aiming for a single digit. However, with the size larger of each fish, the complexity of searching for fishes will be larger. Using Hodoku, the program provides us with UI for searching for fishes. For example, Hodoku provides the option "searching one fish for each elimination (candidate)" to accelerate the running.
I think that my algorithm of searching for them has not been optimized yet. For example, we can use a faster searcher to gather all single-digit eliminations, then check whether the cover sets found contains these eliminations. If not, skip the loop to find another one.