Project Euler Problem 2: Even Fibonacci numbers

Problem 2 asks us to calculate the fibonacci numbers under 4.000.000, and calculate the sum of the even ones. The fibonacci sequence is a sequence of numbers where each number is the sum of the two preceding ones, usually starting with 0 and 1, but in this case the problem has us start with 1 and 2.

A fibonacci calculator is a nice exercise given to students to introduce them to recursion, but in this case, we can solve it using a simple loop. I will create 2 variables holding the last two numbers of the sequence, and a variable to hold the sum of the even numbers. I will then iterate over the sequence, adding the last two numbers to get the next one, and checking if it is even to add it to the sum.

a = 1
b = 2
s = 2 # 2 is the first even number in the sequence and we already added it

while a + b < 4000000:
    tmp = a + b
    a = b
    b = tmp

    s += tmp if tmp % 2 == 0 else 0

print(s)

You can find all my solutions in my GitHub Repository!.

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