gistfile1.aw

<?php

function good_indexes($sequence) {
    $size_of_sequence = count($sequence);
    $sum_lower_indexes = 0;

    for ($i = 0; $i <= $size_of_sequence; $i++)
    {
        if (!isset($sequence[$i]))
        {
            throw new Exception("Index : $i not exists in the sequence");
        }

        $sum_lower_indexes += $sequence[$i];

        $sum_higher_indexes = 0;
        for ($j = $i; $j < $size_of_sequence; $j++)
        {
            $sum_higher_indexes += $sequence[$j];
        }

        if ($sum_lower_indexes == $sum_higher_indexes) {
            echo $i . "\n";
        }
    }
}

$sequence = array(-7, 1, 5, 2, -4, 3, 0);

try {
    good_indexes($sequence);
} catch(Exception $e) {
    echo $e->getMessage();
}