1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
|
<!doctype html>
<html>
<head>
<title>CodeMirror: Haskell mode</title>
<link rel="stylesheet" href="../../lib/codemirror.css">
<script src="../../lib/codemirror.js"></script>
<script src="haskell.js"></script>
<link rel="stylesheet" href="../../theme/elegant.css">
<style type="text/css">.CodeMirror {border-top: 1px solid black; border-bottom: 1px solid black;}</style>
<link rel="stylesheet" href="../../doc/docs.css">
</head>
<body>
<h1>CodeMirror: Haskell mode</h1>
<form><textarea id="code" name="code">
module UniquePerms (
uniquePerms
)
where
-- | Find all unique permutations of a list where there might be duplicates.
uniquePerms :: (Eq a) => [a] -> [[a]]
uniquePerms = permBag . makeBag
-- | An unordered collection where duplicate values are allowed,
-- but represented with a single value and a count.
type Bag a = [(a, Int)]
makeBag :: (Eq a) => [a] -> Bag a
makeBag [] = []
makeBag (a:as) = mix a $ makeBag as
where
mix a [] = [(a,1)]
mix a (bn@(b,n):bs) | a == b = (b,n+1):bs
| otherwise = bn : mix a bs
permBag :: Bag a -> [[a]]
permBag [] = [[]]
permBag bs = concatMap (\(f,cs) -> map (f:) $ permBag cs) . oneOfEach $ bs
where
oneOfEach [] = []
oneOfEach (an@(a,n):bs) =
let bs' = if n == 1 then bs else (a,n-1):bs
in (a,bs') : mapSnd (an:) (oneOfEach bs)
apSnd f (a,b) = (a, f b)
mapSnd = map . apSnd
</textarea></form>
<script>
var editor = CodeMirror.fromTextArea(document.getElementById("code"), {
lineNumbers: true,
matchBrackets: true,
theme: "elegant"
});
</script>
<p><strong>MIME types defined:</strong> <code>text/x-haskell</code>.</p>
</body>
</html>
|
