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Size: a a a
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a = list(range(1, 13))
n = 3
out = [max(x) for x in zip(*[iter(a)] * n)]
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initial = [...]
r = [max(initial[n:n+3]) for n in range(0, len(initial), 3)]
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inp
a = [1,2,3,6,3,2,10,11,12]
out
a = [3,6,12]