146 lines
3.6 KiB
Python
146 lines
3.6 KiB
Python
'''Determine if a string has all unique characters'''
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from itertools import groupby
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# duplicatedCharIndices :: String -> Maybe (Char, [Int])
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def duplicatedCharIndices(s):
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'''Just the first duplicated character, and
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the indices of its occurrence, or
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Nothing if there are no duplications.
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'''
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def go(xs):
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if 1 < len(xs):
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duplicates = list(filter(lambda kv: 1 < len(kv[1]), [
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(k, list(v)) for k, v in groupby(
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sorted(xs, key=swap),
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key=snd
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)
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]))
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return Just(second(fmap(fst))(
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sorted(
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duplicates,
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key=lambda kv: kv[1][0]
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)[0]
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)) if duplicates else Nothing()
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else:
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return Nothing()
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return go(list(enumerate(s)))
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# TEST ----------------------------------------------------
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# main :: IO ()
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def main():
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'''Test over various strings.'''
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def showSample(s):
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return repr(s) + ' (' + str(len(s)) + ')'
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def showDuplicate(cix):
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c, ix = cix
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return repr(c) + (
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' (' + hex(ord(c)) + ') at ' + repr(ix)
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)
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print(
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fTable('First duplicated character, if any:')(
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showSample
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)(maybe('None')(showDuplicate))(duplicatedCharIndices)([
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'', '.', 'abcABC', 'XYZ ZYX',
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'1234567890ABCDEFGHIJKLMN0PQRSTUVWXYZ'
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])
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)
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# FORMATTING ----------------------------------------------
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# fTable :: String -> (a -> String) ->
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# (b -> String) -> (a -> b) -> [a] -> String
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def fTable(s):
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'''Heading -> x display function -> fx display function ->
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f -> xs -> tabular string.
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'''
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def go(xShow, fxShow, f, xs):
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ys = [xShow(x) for x in xs]
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w = max(map(len, ys))
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return s + '\n' + '\n'.join(map(
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lambda x, y: y.rjust(w, ' ') + ' -> ' + fxShow(f(x)),
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xs, ys
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))
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return lambda xShow: lambda fxShow: lambda f: lambda xs: go(
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xShow, fxShow, f, xs
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)
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# GENERIC -------------------------------------------------
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# Just :: a -> Maybe a
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def Just(x):
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'''Constructor for an inhabited Maybe (option type) value.
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Wrapper containing the result of a computation.
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'''
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return {'type': 'Maybe', 'Nothing': False, 'Just': x}
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# Nothing :: Maybe a
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def Nothing():
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'''Constructor for an empty Maybe (option type) value.
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Empty wrapper returned where a computation is not possible.
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'''
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return {'type': 'Maybe', 'Nothing': True}
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# fmap :: (a -> b) -> [a] -> [b]
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def fmap(f):
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'''fmap over a list.
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f lifted to a function over a list.
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'''
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return lambda xs: [f(x) for x in xs]
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# fst :: (a, b) -> a
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def fst(tpl):
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'''First member of a pair.'''
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return tpl[0]
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# head :: [a] -> a
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def head(xs):
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'''The first element of a non-empty list.'''
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return xs[0] if isinstance(xs, list) else next(xs)
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# maybe :: b -> (a -> b) -> Maybe a -> b
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def maybe(v):
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'''Either the default value v, if m is Nothing,
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or the application of f to x,
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where m is Just(x).
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'''
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return lambda f: lambda m: v if (
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None is m or m.get('Nothing')
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) else f(m.get('Just'))
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# second :: (a -> b) -> ((c, a) -> (c, b))
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def second(f):
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'''A simple function lifted to a function over a tuple,
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with f applied only to the second of two values.
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'''
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return lambda xy: (xy[0], f(xy[1]))
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# snd :: (a, b) -> b
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def snd(tpl):
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'''Second member of a pair.'''
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return tpl[1]
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# swap :: (a, b) -> (b, a)
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def swap(tpl):
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'''The swapped components of a pair.'''
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return (tpl[1], tpl[0])
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# MAIN ---
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if __name__ == '__main__':
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main()
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