declare(strict_types=1);
/**
* Finds the element with the minimum occurrences in an array.
*
* @param array<int|string> $array Input array containing int or string scalar values.
* @return int|string|null The least frequent element, or null if the array is empty.
*/
function findMinOccurrence(array $array): int|string|null
{
if (empty($array)) {
return null;
}
// 1. Tally element frequencies (O(N) time complexity)
$counts = array_count_values($array);
// 2. Sort associative array by value ascending while maintaining key associations
asort($counts);
// 3. Extract the key of the first element (the one with the lowest count)
return array_key_first($counts);
}
// Example usage:
$arr = [1, 3, 1, 1, 4, 4, 5, 5, 4, 2, 2, 2, 3, 3, 3];
$result = findMinOccurrence($arr);
if ($result !== null) {
echo $result . PHP_EOL; // Output: 5
} else {
echo "The array was empty." . PHP_EOL;
}
/*
run:
5
*/
