Find the Fulcrum

A fulcrum of a list is an integer such that all elements to the left of it and all elements to the right of it sum to the same value. Write a function that finds the fulcrum of a list.

To illustrate:

find_fulcrum([3, 1, 5, 2, 4, 6, -1]) ➞ 2
// Since [3, 1, 5] and [4, 6, -1] both sum to 9

Examples

find_fulcrum([1, 2, 4, 9, 10, -10, -9, 3]) ➞ 4

find_fulcrum([9, 1, 9]) ➞ 1

find_fulcrum([7, -1, 0, -1, 1, 1, 2, 3]) ➞ 0

find_fulcrum([8, 8, 8, 8]) ➞ -1

Notes

• If the fulcrum does not exist, return -1 (see example #4).
• Exclude the leftmost and rightmost elements when computing the fulcrum (it doesn't make sense to sum zero values).
• If a list has multiple fulcrums, return the one that occurs first.