fish :: [Int] -> [Int] -> Int
fish a b = size - dead
  where
    size      = length a
    (dead, _) = foldl step (0, []) (zip a b)

    step (d, stack) (ai, bi)
      | bi == 1   = (d, ai : stack)
      | otherwise = fight ai stack d

    fight _  []             d = (d, [])
    fight ai (top : tops) d
      | ai > top  = fight ai tops (d + 1)
      | otherwise = (d + 1, top : tops)