Python/project_euler/problem_001/sol3.py

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"""
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Problem Statement:
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.
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Find the sum of all the multiples of 3 or 5 below N.
"""
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def solution(n: int = 1000) -> int:
"""
This solution is based on the pattern that the successive numbers in the
series follow: 0+3,+2,+1,+3,+1,+2,+3.
Returns the sum of all the multiples of 3 or 5 below n.
>>> solution(3)
0
>>> solution(4)
3
>>> solution(10)
23
>>> solution(600)
83700
"""
total = 0
num = 0
while 1:
num += 3
if num >= n:
break
total += num
num += 2
if num >= n:
break
total += num
num += 1
if num >= n:
break
total += num
num += 3
if num >= n:
break
total += num
num += 1
if num >= n:
break
total += num
num += 2
if num >= n:
break
total += num
num += 3
if num >= n:
break
total += num
return total
if __name__ == "__main__":
print(solution(int(input().strip())))