Problem: three piece puzzle

Code: three+piece+puzzle/tails_1700550246

Nibbles version: 0.2 | 0.21 | 0.22 | 0.23 | 0.24 | 0.25 | 1.00

Format: Compact | Simple | +Type | Table | JSON | .nbl (DeBruijn) | .nbl (names)

+ (concat) 
    + (concat) 
        =~ (group by (also sorts)) 
            % (split (remove empties)) 
                @ (= fstLine) 
                ~ (auto = words) 
            / (foldr1) <--arg( A ) 
                . (map) 
                    $ (= A) 
                    , (length) <--arg( B ) 
                        `% (split list (keep empties)) 
                            ;$ (= fstLine) 
                            $ (= B) 
                - (subtract) <--arg( D C ) 
                    (implicit arg = D) 
                    (implicit arg = C)