OddOccurrencesInArray.php

<?php

/*
Find value that occurs in odd number of elements.
*/
function oddOccurrencesInArray(array $arr) : int
{
    foreach(array_count_values($arr) as $number => $count) {
        if ($count % 2) {
            return $number;
        }
    }
    
    return 0;
}

$test = [9, 3, 9, 3, 9, 7, 9];

print_r(oddOccurrencesInArray($test)); // Result: 7

Congratulations on your solution! I was not aware of the array_count_values function, so I had to implement something similar that worked, but not with the desired performance. Thank you for sharing your code.