如何將合並列表按升序排序？

Question

merge :: [a] -> [a] -> [a]

 merge xs     []     = xs
 merge []     ys     = ys
 merge (x:xs) (y:ys) = x : y : merge xs ys

我已經開始工作了，但是現在我需要按升序對它們進行排序。

Answer 1

您只需要比較x和y並確定要先添加到結果中。 請注意，一次只能添加一個 。 x之后的下一個元素可能仍在y之前。

注意：您所需要的Ord約束，以確保<=被定義為a 。

merge :: Ord a => [a] -> [a] -> [a]
merge xs [] = xs
merge [] ys = ys
merge xs@(x:xs') ys@(y:ys') | x <= y = x : merge xs' ys
                            | otherwise = y : merge xs ys'