Question

I am new to Python language, and I am running into this problem, the code below is not returning the expecting value:

def rabbits(n):
    first = 1
    second = 1

    if n == 1 or n == 2:
        return 1
    while n > 2:
        first, second = second, first + second
        n -= 1

    if n > 5:
        die1 = 1
        die2 = 1
        if n == 6 or n == 7:
            return second - 1
        while n > 7:
            die1, die2 = die2, die1 + die2
            n -= 1
        return second - die2
    return second

I am hoping that rabbits(6) would be returning 7, but it returns 8 instead. Can anyone help me find the wrong stuff in here? Thanks!

Answer 1

You first reduce n to 2 or lower (while n > 2: .. n -= 1), then test if n > 5.

That latter test is never going to pass because n will now always be 2 or lower.

That first reduction calculates the fibonacci sequence, and the 6th value in that sequence is 8 (after 1, 1, 2, 3 & 5).

To avoid your problem, use a simple range loop instead:

for i in range(n, 2, -1):
    first, second = second, first + second

Now i will go from 6 to 3 without changing n.