C 版打印特殊矩阵问题的 Haskell 实现

Question

问题描述见 http://bbs.chinaunix.net/thread-1279897-1-1.html

Haskell 实现:

2. module Main where
4. import System.Environment (getArgs)
5. import Data.List (intersperse)
7. -- | before or after part
8. bafix :: Bool -> Int -> [[Int]]
9. bafix isBefore n = map ba [1,3..c]
10.     where
11.         ba :: Int -> [Int]
12.         ba m = prefix ++ middle ++ (reverse prefix)
13.             where
14.                 prefix = [1..m]
15.                 middle = replicate (n - 2 * m) p
16.                 p      = if isBefore then (m+1) else m
18.         c      = floor $ (fromIntegral n) / 2
20. -- | Before part
21. beforePart :: Int -> [[Int]]
22. beforePart n = bafix True n
24. -- | After part
25. afterPart :: Int -> [[Int]]
26. afterPart n = reverse $ bafix False n
28. -- | Middle part
29. middlePart :: Int -> [[Int]]
30. middlePart n = replicate m $ digitPalindrom n
31.     where
32.         m = n - 2 * (length [1,3..c])
33.         c = floor $ (fromIntegral n) / 2
35.         digitPalindrom :: Int -> [Int]
36.         digitPalindrom u = [1..c] ++ (reverse [1..f])
37.             where
38.                 u' = fromIntegral u
39.                 c  = ceiling $ u' / 2
40.                 f  = floor   $ u' / 2
42. -- | matrix
43. matrix :: Int -> [[Int]]
44. matrix n = beforePart n ++ middlePart n ++ afterPart n
46. -- | show matrix
47. showMatrix :: [[Int]] -> String
48. showMatrix nss = unlines $ map (ns -> concat $ intersperse " " $ map show ns) nss
50. -- | main
51. main = do
52.     args <- getArgs
53.     let n = read $ args !! 0
54.     putStrLn $ showMatrix $ matrix n

复制代码

ACA80110:tmp lee$ ./matrix 7
1 2 2 2 2 2 1
1 2 3 4 3 2 1
1 2 3 4 3 2 1
1 2 3 4 3 2 1
1 2 3 4 3 2 1
1 2 3 3 3 2 1
1 1 1 1 1 1 1

ACA80110:tmp lee$ ./matrix 8
1 2 2 2 2 2 2 1
1 2 3 4 4 3 2 1
1 2 3 4 4 3 2 1
1 2 3 4 4 3 2 1
1 2 3 4 4 3 2 1
1 2 3 4 4 3 2 1
1 2 3 3 3 3 2 1
1 1 1 1 1 1 1 1