Codility TapeEquality O(n)

codility-1_1.php

<?php

/**
 * @param  array $A
 * @return int
 */
function solution(array $A)
{
    $left = $A[0];
    $right = array_sum($A) - $left;
    $min = abs($left - $right);

    $keys = count($A);
    
    for ($i = 1; $i < $keys - 1; $i++) {
        $left += $A[$i];
        $right -= $A[$i];
        $diff = abs($left - $right);
        $min = ($diff < $min) ? $diff : $min;
    }
    
    return $min;
}