problem_001.py

# Project Euler Problem 1: Multiples of 3 and 5
"""
If we list all the natural numbers below 10 that are multiples of 3 or 5,
we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.
"""

# Brute -force approach
# Count from 1 to 1000, check if number is divisible by 3 or 5. if true, add to sum.
def sum_of_multiples_bf(limit):
    sum = 0
    for a in range(1,limit):
        if(a % 3 == 0 or a % 5 == 0):
            sum += a
    return sum
print(sum_of_multiples_bf(1000))

# Find multiples of 3 and 5, subtract numbers that are counted twice.
def sum_of_multiples_ms(limit):
    sum = 0
    for i in range(3,limit,3):
        sum += i
    for j in range(5,limit,5):
        sum += j
    for k in range(15, limit, 15):
        sum -= k
    return sum
print(sum_of_multiples_ms(1000))