Codility is one of the most common services used to apply test codes (for job applications, for example). Here you can find a task sample to pratice before try the real test. The present sample is the Equi Task, and the propose is very simple.

Imagine an array with N elements. There is a P value (0 <= P <= N) who solve the problem below?

```
A[0] + A[1] + ... + A[P−1] = A[P+1] + ... + A[N−2] + A[N−1].
```

In other words, where is the equilibrium index of this array?

For example, consider the following array A consisting of N = 7 elements:

```
A[0] = -7 A[1] = 1 A[2] = 5
A[3] = 2 A[4] = -4 A[5] = 3
A[6] = 0
```

P = 3 is an equilibrium index of this array, because:

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

The task is build one subroutine called equi who will receive the array should return the value of P, or -1 if there is no equilibrium index.

Easy? Well, there is another challenge: create a O(n) solution.

Here is my solution in Perl: