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