<?php

/**

* Deduplicates an array of strings, returning a new array with unique values.

* Outputs error messages if input is invalid.

*

* @param array $stringArray The array of strings to deduplicate.

* @return array|string A new array with unique strings, or an error message.

*/

function deduplicateStrings(array $stringArray): array|string

{

if (!is_array($stringArray)) {

return "Error: Input must be an array.";

}

if (empty($stringArray)) {

return []; // Return empty array if input is empty

}

$uniqueStrings = [];

$seen = []; // Use an associative array for faster lookup

foreach ($stringArray as $string) {

if (!is_string($string)) {

return "Error: Array must contain only strings.";

}

if (!in_array($string, $seen, true)) { // strict type checking

$uniqueStrings[] = $string;

$seen[] = $string;

}

}

return $uniqueStrings;

}

// Example usage (and error handling demonstrations)

$strings1 = ["apple", "banana", "apple", "orange", "banana"];

$result1 = deduplicateStrings($strings1);

echo "Result 1: " . print_r($result1, true) . "\n";

$strings2 = []; // Empty array

$result2 = deduplicateStrings($strings2);

echo "Result 2: " . $result2 . "\n";

$strings3 = ["apple", 123, "banana"]; // Array with non-string

$result3 = deduplicateStrings($strings3);

echo "Result 3: " . $result3 . "\n";

$strings4 = "not an array"; // Not an array

$result4 = deduplicateStrings($strings4);

echo "Result 4: " . $result4 . "\n";

$strings5 = ["apple", "Apple"]; // Case sensitive

$result5 = deduplicateStrings($strings5);

echo "Result 5: " . print_r($result5, true) . "\n";

?>