# Find Equilibrium Index of an Array

**Problem**: Given an array of N integers. You have to find the equilibrium index in this array. Please note – an equilibrium index is that index of an array where sum of elements to the left of that index is equal to sum of elements to the right of that index.

**Problem Explanation:** You are given an array **a ={-7, 1, 5, 2, -4, 3, 0} – **So, here sum of elements to the left of **2** are equal to sum of elements to its right. Similarly, sum of elements to the left of **0** are equal to 0 (please note, sum of elements to the right of **0** are also equal to 0 as there is not element present to its right). Hence, **3** [array index for element 2] and **6** [array index for element 0] are equilibrium index of a.

**Java Implementation**

public void findIndexEquilibrium(int A[], int n) { int sumOfArrayElements = 0; int leftSum = 0; for (int i = 0; i < n; i++) { sumOfArrayElements = sumOfArrayElements + A[i]; } for (int i = 0; i < n; i++) { sumOfArrayElements -= A[i]; if (sumOfArrayElements == leftSum) { System.out.println("Equilibrium index of A[]:" + i); } leftSum += A[i]; } }

**Time Complexity: O(n) **

Note: If you find any other better way to approach to this problem or you find any issue/error in above code snippets/approaches – please share it in the comments section below and get a chance to enrol free of cost for an online Live Data Structure and Algorithm course (specially designed for interview preparation for software companies like Amazon, Google, Facebook, FlipKart, SnapDeal, HealthKart…)