// Enable strict typing for predictable type safety
declare(strict_types=1);
/**
* Reverses only the alphabetic characters in a character array in-place,
* leaving special characters, spaces, and digits in their original positions.
*
* @param array<int, string> $chars Reference to the character array (vector).
*/
function reverseOnlyLetters(array &$chars): void {
$left = 0;
$right = count($chars) - 1;
// Use a two-pointer approach moving inward from both ends
while ($left < $right) {
// Advance left pointer until it points to an alphabetic character
while ($left < $right && !ctype_alpha($chars[$left])) {
$left++;
}
// Move right pointer backward until it points to an alphabetic character
while ($left < $right && !ctype_alpha($chars[$right])) {
$right--;
}
// Swap the valid letters found at both pointers
if ($left < $right) {
$temp = $chars[$left];
$chars[$left] = $chars[$right];
$chars[$right] = $temp;
$left++;
$right--;
}
}
}
// Input string specified
$inputString = "a#b$%c&*(def!";
// Convert the string into an array of single-character strings (acting as a character vector)
$charVector = str_split($inputString);
echo "Original: " . implode('', $charVector) . PHP_EOL;
// Apply the reversal function in-place
reverseOnlyLetters($charVector);
// Reconstruct and display the final string
echo "Reversed: " . implode('', $charVector) . PHP_EOL;
/*
run:
Original: a#b$%c&*(def!
Reversed: f#e$%d&*(cba!
*/
