Equilibrium Index Problem Statement

Given an array Arr consisting of N integers, your task is to find the equilibrium index of the array.

An index is considered as an equilibrium index if the sum of elements of the array to the left of that index is equal to the sum of elements to the right of it.

Input:

The first line contains an integer T, representing the number of test cases.
The first line of each test case contains an integer N, representing the size of the array.
The second line of each test case contains N space-separated integers representing the array elements.

Output:

The output for each test case should be a single integer indicating the equilibrium index of the array.

Example:

Input:
1
5
-7 1 5 2 -4

Output:
2

Explanation:

The index 2 is an equilibrium index because the sum of elements on its left (-7 + 1) equals the sum of elements on its right (2 - 4).

Constraints:

• 1 <= T <= 50
• 1 <= N <= 10^5
• -10^4 <= Arr[i] <= 10^4

Note:

• The array uses 0-based indexing, so return the 0-based index of the equilibrium.
• The element at the equilibrium index is not considered in the sum for either side.
• If multiple indices meet the condition, return the left-most one.
• If no such index is present, return -1.