42 lines
909 B
Python
42 lines
909 B
Python
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# take-aways:
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# - Use integers as lists of boolean values
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# - Use 1 << n to compute 2^n where n = len(xs)
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def set_from_int(xs, n):
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result = []
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for i in range(len(xs)):
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if n & (1 << i) != 0:
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result.append(xs[i])
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return result
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# subsets :: Set a -> List (Set a)
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def subsets(xs):
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n = len(xs)
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return [set_from_int(xs, i) for i in range(1 << n)]
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# 0 1 2
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# 0 N Y Y
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# 1 _ N Y
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# 2 _ _ N
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# For my interview, be able to compute *permutations* and *combinations*
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# This differs from permutations because this is about finding combinations...
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#
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# bottom-up
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# 0 => { }
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# 1 => {3} {4} {3}
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# 2 => {5,4} {5,3} {4,3}
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xs = [
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([], [[]]),
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([5], [[], [5]]),
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([5,4], [[],[5],[4],[5,4]]),
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]
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for x, expected in xs:
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result = subsets(x)
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print("subsets({}) => {} == {}".format(x, result, expected))
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assert result == expected
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print("Success!")
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