Python/project_euler/problem_002/sol5.py

"""
Problem:
Each new term in the Fibonacci sequence is generated by adding the previous two
terms. By starting with 1 and 2, the first 10 terms will be:

    1,2,3,5,8,13,21,34,55,89,..

By considering the terms in the Fibonacci sequence whose values do not exceed
n, find the sum of the even-valued terms. e.g. for n=10, we have {2,8}, sum is
10.
"""


def solution(n: int = 4000000) -> int:
    """Returns the sum of all fibonacci sequence even elements that are lower
    or equals to n.

    >>> solution(10)
    10
    >>> solution(15)
    10
    >>> solution(2)
    2
    >>> solution(1)
    0
    >>> solution(34)
    44
    """

    fib = [0, 1]
    i = 0
    while fib[i] <= n:
        fib.append(fib[i] + fib[i + 1])
        if fib[i + 2] > n:
            break
        i += 1
    total = 0
    for j in range(len(fib) - 1):
        if fib[j] % 2 == 0:
            total += fib[j]

    return total


if __name__ == "__main__":
    print(solution(int(input().strip())))