superpollo writes:
> goal (from e.c.m.): evaluate
> 1^2+2^2+3^2-4^2-5^2+6^2+7^2+8^2-9^2-10^2+...-2010^2, where each three
> consecutive + must be followed by two - (^ meaning ** in this context)
>
> my solution:
>
> >>> s = 0
> >>> for i in range(1, 2011):
> ... s += i**2
> ... if not (i+1)%5:
> ... s -= 2*i**2
> ... if not i%5:
> ... s -= 2*i**2
> ...
> >>> print s
> 536926141
> >>>
>
> bye
Me two:
s = 0
for k in range(1, 2010, 5):
s += k**2 + (k + 1)**2 + (k + 2)**2 - (k + 3)**2 - (k + 4)**2
s = 0
for k in range(1, 2011):
s += k**2 * (-1 if k % 5 in {4,0} else +1)
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