Question

Given an array, I would like to find an index, that the numbers before it, and the numbers after it gives equal sum.

for example an array like
[4,5,6,11,7,8]

output is index 3 because 4+5+6 = 7+8

Answer 1

First find sum of all items, save it as sum, then read from start of array and sum up items to arrive to (sum - current index value)/2, if you didn’t get such result, means there isn’t such an index, also if you get sum/2 in each index of iteration, means related index is your answer.

Sample: 4,5,6,11,7,8
sum = 41.

check index 0: currentSum  = 4, currentSum - currentValue = 4-4 != (41 - 4)/2
check index 1: currentSum  =  9, currentSum - currentValue = 9-5 != (41 - 5)/2
check index 2: currentSum  = 15, currentSum - currentValue = 15-6 != (41 - 6)/2
check index 3: currentSum  = 26, currentSum - currentValue = 15 == (41 - 11)/2