You are going to be given an array of integers. Your job is to take that array and find an index N where the sum of the integers to the left of N is equal to the sum of the integers to the right of N. If there is no index that would make this happen, return `-1`.
__For example:__
Let's say you are given the array `{1,2,3,4,3,2,1}`:  
Your function will return the index `3`, because at the 3rd position of the array, the sum of left side of the index (`{1,2,3}`) and the sum of the right side of the index (`{3,2,1}`) both equal `6`.
Let's look at another one.  
You are given the array `{1,100,50,-51,1,1}`:  
Your function will return the index `1`, because at the 1st position of the array, the sum of left side of the index (`{1}`) and the sum of the right side of the index (`{50,-51,1,1}`) both equal `1`.
Last one:  
You are given the array `{20,10,-80,10,10,15,35}`  
At index 0 the left side is `{}`  
The right side is `{10,-80,10,10,15,35}`  
They both are equal to `0` when added. (Empty arrays are equal to 0 in this problem)  
Index 0 is the place where the left side and right side are equal.  
Note: Please remember that in most programming/scripting languages the index of an array starts at 0.
__Input:__  
An integer array of length `0 < arr < 1000`. The numbers in the array can be any integer positive or negative.
__Output:__  
The lowest index `N` where the side to the left of `N` is equal to the side to the right of `N`. If you do not find an index that fits these rules, then you will return `-1`.
__Note:__  
If you are given an array with multiple answers, return the lowest correct index.
def find_even_index(arr):
    left_sum, right_sum = 0, sum(arr)

    for i, n in enumerate(arr):
        right_sum -= n
        if left_sum == right_sum:
            return i
        left_sum += n

    return -1

def find_even_index(arr):
    left_sum, right_sum = 0, sum(arr)

    for i, n in enumerate(arr):
        right_sum -= n
        if left_sum == right_sum:
            return i
        left_sum += n

    return -1
