Python solutions to Project Euler Problem 1

euler1.py

"""Find the sum of all numbers below 1000 divisible by 3 or 5.
http://projecteuler.net/index.php?section=problems&id=1"""

#Brute force #1 
sum(x for x in xrange(3,1000) if x % 3 == 0 or x % 5 == 0)

#Brute force #2
sum(set(range(3, 1000, 3) + range(5, 1000, 5)))

#Less brute (after reading the problem discussion PDF)
T = 1000
def sum_divisible_by(n):
  p = T // n
  return n * (p * (p + 1)) // 2

sum(sum_divisible_by(n) for n in (3, 5, -15))