find first positive number which is not in an numerical array

find_first_positive_number_not_in_array.php

<?php
// you can write to stdout for debugging purposes, e.g.
// print "this is a debug message\n";

function solution($A) {
    // write your code in PHP7.0
    $arr_checker = range(1, 100000);

    $A = array_unique($A, SORT_NUMERIC );
    sort($A);
    $A = array_intersect($A, $arr_checker);
    $A = array_values($A);
    $A = array_diff($arr_checker, $A);
    return reset($A);
}
print "testing....\n";
$A =  [-1,-8, 1, 3, 6, 99999, 4, 1, 2];
$result = solution($A);
print  "array:" . print_r($A, true). "\nresult: $result\n\n";

For the demo task https://app.codility.com/c/run/demoZ8PATM-3DF