Question

str_repeat(A, B) repeat string A, B times:

$string = "This is a " . str_repeat("test", 2) . 
          "! " . str_repeat("hello", 3) . " and Bye!";  

// Return "This is a testtest! hellohellohello and Bye!"

I need reverse operation:

str_shrink($string, array("hello", "test")); 
// Return "This is a test(x2)! hello(x3) and Bye!" or
//        "This is a [test]x2! [hello]x3 and Bye!"

Best and efficient way for create str_shrink function?

Answer 1

Here are two versions that I could come up with.

The first uses a regular expression and replaces duplicate matches of the $needle string with a single $needle string. This is the most vigorously tested version and handles all possibilities of inputs successfully (as far as I know).

function str_shrink( $str, $needle)
{
    if( is_array( $needle))
    {
        foreach( $needle as $n)
        {
            $str = str_shrink( $str, $n);   
        }
        return $str;
    }
    $regex = '/(' . $needle . ')(?:' . $needle . ')+/i';
    return preg_replace_callback( $regex, function( $matches) { return $matches[1] . '(x' . substr_count( $matches[0], $matches[1]) . ')'; }, $str);
}

The second uses string manipulation to continually replace occurrences of the $needle concatenated with itself. Note that this one will fail if $needle.$needle occurs more than once in the input string (The first one does not have this problem).

function str_shrink2( $str, $needle)
{
    if( is_array( $needle))
    {
        foreach( $needle as $n)
        {
            $str = str_shrink2( $str, $n);   
        }
        return $str;
    }
    $count = 1; $previous = -1;
    while( ($i = strpos( $str, $needle.$needle)) > 0)
    {
        $str = str_replace( $needle.$needle, $needle, $str);
        $count++;
        $previous = $i;
    }
    if( $count > 1)
    {
        $str = substr( $str, 0, $previous) . $needle .'(x' . $count . ')' . substr( $str, $previous + strlen( $needle));
    }
    return $str;
}

See them both in action

Edit: I didn’t realize that the desired output wanted to include the number of repetitions. I’ve modified my examples accordingly.