Equilibrium Point in an Array

gistfile1.php

<?php 
function equi ( $A ) {
    $countA = count($A);
    $forwardSum = array();
    $backwardSum = array();
    for ($i = 0; $i < $countA; $i++) {
        if ($i == 0) {
            //$forwardSum[$i] = $A[$i];
            $forwardSum[0] = 0;
        } else {
            $forwardSum[$i] = $forwardSum[$i - 1] + $A[$i-1];
        }
    }
    
    for ($i = ($countA - 1); $i >= 0; $i--) {
        if ($i == ($countA - 1)) {
            //$backwardSum[$i] = $A[$i];
            $backwardSum[$i] = 0;
        } else {
            $backwardSum[$i] = $backwardSum[$i + 1] + $A[$i+1];
        }
    }
    $intersects = (array_intersect_assoc($forwardSum, $backwardSum));
    if (count($intersects)) {
        return key($intersects);
    }
    
    return -1;
}