Find Equilibrium index of an array

Equilibrium index of an array is an index such that the sum of elements at lower indexes is equal to the sum of elements at higher indexes.

For example, in an array A:

Input : A[] = {-7, 1, 5, 2, -4, 3, 0}
Output : 3

3 is an equilibrium index, because:

A[0] + A[1] + A[2] = A[4] + A[5] + A[6]

Write a function int equilibrium(int[] arr, int n); that given a sequence arr[] of size n, returns an equilibrium index (if any) or -1 if no equilibrium indexes exist.

[neelkusumekka]

Apart from index 3, we also have another equilibrium index at 6. This program is just fetching for index 3.

[zipzap]

Quite heavy on performance... You can do it in logn