我需要找到矩阵中最小的元素。 我有一个解决方案,但不是完美的。
type Matrix = [[Int]]
matMin :: Matrix -> Int
matMin [] = 99999999999
matMin (xs:xss) = minimum xs `min` matMin xss
有没有人能给我一个更好的解决方案的提示?
matMin = minimum . concat
。请看map
函数。矩阵的最小值是每行最小值中的最小值:
Prelude> :t minimum . map minimum
minimum . map minimum :: Ord c => [[c]] -> c
稍微调整一下您的代码,避免使用硬编码的值:
type Matrix = [[Int]]
matMin :: Matrix -> Int
matMin [] = error "min is undefined for 0x0 matrix"
matMin [xs] = minimum xs
matMin (xs:xss) = minimum xs `min` matMin xss
maxBound
代替(因为Int
是Bounded
)。matMin :: Matrix -> Int
matMin [] = maxBound
matMin (xs:xss) = minimum xs `min` matMin xss
matMin = foldl' (acc x -> minimum x `min` acc) maxBound
matMin = foldl' (flip (min . minimum)) maxBound
-- or if you don't like the flip
matMin = foldr (min . minimum) maxBound
matFoldr :: (b -> c -> c) -- how to merge the accumulator with the result of mergeCells
-> ([a] -> b) -- how to merge a row of cells
-> c -- a starting accumulator value
-> [[a]] -- the matrix to fold over
-> c
matFoldr mergeRows mergeCells start = foldr (mergeRows . mergeCells) start
matMin = matFoldr min minimum maxBound
matMax = matFoldr max maximum minBound
matSum = matFoldr (+) sum 0
matProduct = matFoldr (*) product 1
如果我们真的真的想要,甚至可以做到您无需指定要使用哪个列表操作。
matEasyFold mergeRows start = matFoldr mergeRows mergeCells start
where mergeCells = foldr mergeRows start
matMin = matEasyFold min maxBound
matSum = matEasyFold (+) 0
-- etc
非常感谢 :-p 我解决得更容易,但它与Mihai的答案非常相似
matMin :: Matrix -> Int
matMin xss = minimum(map minimum xss)
感谢您的帮助。