How to find the sum of two numbers in an array that match the input value

You can test each position, at the beginning and at the end of the array, and then test each position and increment as you find the desired value:

<?php
function getPairNumbers($numbers, $target)
{
    $result = array();
    sort($numbers);
    $high = count($numbers) - 1;

    for ($i = 0; $i < count($numbers);) {
        if ($numbers[$i] + $numbers[$high] == $target) {
            $result[0] = $numbers[$i];
            $result[1] = $numbers[$high];
            break;
        }

        if ($numbers[$i] + $numbers[$high] < $target) {
            $i++;
         }

        if ($numbers[$i] + $numbers[$high] > $target) {
            $high--;
        }

        if ($high <= $i) {
            return null;
        }
    }

    return $result;
}

$arr = getPairNumbers(array(1,4,5,15,30,25,20,0,13), 18);

print_r($arr);