PHP Program to print all permutations of a given string

<?php 
// PHP program to print all 
// permutations of a given string. 

/* Permutation function @param 
   str string to calculate permutation 
   for @param l starting index @param 
   r end index */
function permute($str, $l, $r) 
{ 
    if ($l == $r) 
        echo $str. "\n"; 
    else
    { 
        for ($i = $l; $i <= $r; $i++) 
        { 
            $str = swap($str, $l, $i); 
            permute($str, $l + 1, $r); 
            $str = swap($str, $l, $i); 
        } 
    } 
} 

/* Swap Characters at position @param 
   a string value @param i position 1 
   @param j position 2 @return swapped 
   string */
function swap($a, $i, $j) 
{ 
    $temp; 
    $charArray = str_split($a); 
    $temp = $charArray[$i] ; 
    $charArray[$i] = $charArray[$j]; 
    $charArray[$j] = $temp; 
    return implode($charArray); 
} 

// Driver Code 
$str = "ABC"; 
$n = strlen($str); 
permute($str, 0, $n - 1); 

// This code is contributed by mits. 
?>