sol4.py

"""
Project Euler Problem 2: https://projecteuler.net/problem=2

Even Fibonacci Numbers

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
four million, find the sum of the even-valued terms.

References:
 - https://en.wikipedia.org/wiki/Fibonacci_number
"""

importmath
fromdecimalimportDecimal, getcontext


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

 >>> solution(10)
 10
 >>> solution(15)
 10
 >>> solution(2)
 2
 >>> solution(1)
 0
 >>> solution(34)
 44
 >>> solution(3.4)
 2
 >>> solution(0)
 Traceback (most recent call last):
 ...
 ValueError: Parameter n must be greater than or equal to one.
 >>> solution(-17)
 Traceback (most recent call last):
 ...
 ValueError: Parameter n must be greater than or equal to one.
 >>> solution([])
 Traceback (most recent call last):
 ...
 TypeError: Parameter n must be int or castable to int.
 >>> solution("asd")
 Traceback (most recent call last):
 ...
 TypeError: Parameter n must be int or castable to int.
 """

try:
n=int(n)
except (TypeError, ValueError):
raiseTypeError("Parameter n must be int or castable to int.")
ifn<=0:
raiseValueError("Parameter n must be greater than or equal to one.")
getcontext().prec=100
phi= (Decimal(5) **Decimal("0.5") +1) /Decimal(2)

index= (math.floor(math.log(n* (phi+2), phi) -1) //3) *3+2
num=Decimal(round(phi**Decimal(index+1))) / (phi+2)
total=num//2
returnint(total)


if__name__=="__main__":
print(f"{solution() =}")