How to display even Fibonacci numbers by specifying their number?-CodePudding

I have a function that checks Fibonacci numbers for even.

def fibonacci(num=4):
    fib1 = fib2 = 1
    print(0, end=' ')
    for i in range(1, num):
        fib1, fib2 = fib2, fib1   fib2
        if (fib2 % 2) == 0:
            print(fib2, end=' ')

fibonacci()

I need it to output a specified number of even numbers

Example input: 4

Example output: 0 2 8 34

CodePudding user response：

You could make your fibonacci function a generator that only yields even Fibonacci numbers, and then just pull the desired number of values from it:

def even_fibonacci():
    fib1, fib2 = 0, 1
    while True:
        if fib1 % 2 == 0:
            yield fib1
        fib1, fib2 = fib2, fib1   fib2


it = even_fibonacci()
for _ in range(4):
    print(next(it))

prints:

CodePudding user response：

You could just go over the even ones directly:

def fibonacci(num=4):
    fib1, fib2 = 1, 0
    for _ in range(num):
        print(fib2, end=' ')
        fib1, fib2 = fib1   2*fib2, 2*fib1   3*fib2

Consider two adjacent Fibonacci numbers a and b (initially 1 and 0) and what happens when you shift the window:

   a     b    # odd even
   b   a b    # even odd
 a b  a 2b    # odd odd
a 2b 2a 3b    # odd even

So every third Fibonacci number is even and that last line also tells you how to shift by three steps directly.

CodePudding user response：

Use while loop instead.

def fibonacci(count=4):
    fib1 = fib2 = 1
    i = 1
    print(0, end=' ')
    while i < count:
        fib1, fib2 = fib2, fib1   fib2
        if (fib2 % 2) == 0:
            print(fib2, end=' ')
            i  =1

fibonacci()

Output: 0 2 8 34