PHP Program to print all permutations of a given string

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A permutation also called an “arrangement number” or “order,” is a rearrangement of the elements of an ordered list S into a one-to-one

A permutation also called an “arrangement number” or “order,” is a rearrangement of the elements of an ordered list S into a one-to-one correspondence with S itself. A string of length n has n! permutation.

Source: Mathword(http://mathworld.wolfram.com/Permutation.html)

Below are the permutations of string ABC.
ABC ACB BAC BCA CBA CAB

Here is a solution that is used as a basis in backtracking.

PHP

<?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.  
?>  

Output:

ABC
ACB
BAC
BCA
CBA
CAB

Algorithm Paradigm: Backtracking

Time Complexity: O(n*n!) Note that there are n! permutations and it requires O(n) time to print a permutation.

Auxiliary Space: O(r – l)

Note: The above solution prints duplicate permutations if there are repeating characters in the input string. Please see the below link for a solution that prints only distinct permutations even if there are duplicates in input.
Print all distinct permutations of a given string with duplicates.
Permutations of a given string using STL