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38 lines
1.3 KiB
Python
38 lines
1.3 KiB
Python
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import random
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class RandomCycler:
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"""
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Creates an internal copy of a sequence and allows access to its items in a constrained random
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order. For a source sequence of n items and one or several consecutive queries of a total
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of m items, the following guarantees hold (one implies the other):
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- Each item will be returned between m // n and ((m - 1) // n) + 1 times.
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- Between two appearances of the same item, there may be at most 2 * (n - 1) other items.
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"""
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def __init__(self, source):
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if len(source) == 0:
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raise Exception("Can't create RandomCycler from an empty collection")
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self.all_items = list(source)
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self.next_items = []
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def sample(self, count: int):
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shuffle = lambda l: random.sample(l, len(l))
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out = []
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while count > 0:
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if count >= len(self.all_items):
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out.extend(shuffle(list(self.all_items)))
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count -= len(self.all_items)
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continue
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n = min(count, len(self.next_items))
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out.extend(self.next_items[:n])
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count -= n
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self.next_items = self.next_items[n:]
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if len(self.next_items) == 0:
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self.next_items = shuffle(list(self.all_items))
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return out
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def __next__(self):
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return self.sample(1)[0]
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