Triplet in array that sum to a given value.

<?php

// Write a function that finds a triplet from an array that sum to a given value.
// Complexity: O(n2)

function findTriplet($array, $sum)
{
    if (count($array) < 3) return null;

    for ($i = 0; $i < count($array) - 2; $i++) {
        $firstItem = $array[$i];
        $seenList = [];

        for ($j = $i + 1; $j < count($array); $j++) {
            $thirdItem = $array[$j];
            $secondItem = $sum - ($firstItem + $thirdItem);

            if (isset($seenList[$secondItem])) {
                return [$firstItem, $secondItem, $thirdItem];
            }

            $seenList[$thirdItem] = '';
        }
    }

    return null;
}