how to get all possible combinations of digits until 789?

Im trying to write algorithm to get all combinations and increment by one at a same time and get this

function generate($index){
    $xxx = '';
    $flag = 0;  
    $lengtchString = strlen($index); 
    for($y = 0; $y != $lengtchString; $y++) {
        $xxx .= "$y";
    }
    while ($flag != $lengtchString ) 
    { 
        for ($i = 0; $i<$lengtchString-1; $i++) 
        {            
            $temp = $xxx[$i];  
            $xxx[$i] = $xxx[$i+1]; 
            $xxx[$i+1] = $temp;   
            echo $xxx."<br>"; 
        } 
        $flag++; 
    }
}
generate('abc');

and output is

I need to get all combinations not only for 3 digits but also all combinations .

For example if I write 'abc'... I need output like

and so on.... untill 789 in condition that digits wouldnt repeat... my mind actually to be blown, cant get proper algorithm for that. thanks in advance

Solution

Check this link PHP algorithm to generate all combinations of a specific size from a single set

    <?php
    function sampling($chars, $size, $combinations = array()) {
    $charsArray = str_split($chars);
    # if it's the first iteration, the first set 
    # of combinations is the same as the set of characters
    if (empty($combinations)) {
        $combinations = $charsArray;
    }

    # we're done if we're at size 1
    if ($size == 1) {
        return $combinations;
    }

    # initialise array to put new values in
    $new_combinations = array();

    # loop through existing combinations and character set to create strings
    foreach ($combinations as $combination) {
        foreach ($charsArray as $char) {
            $new_combinations[] = $combination . $char;
        }
    }
    # call same function again for the next iteration
    return sampling($chars, $size - 1, $new_combinations);

}

// example

$output = sampling("0123456789", 3);
print "<pre>";print_r($output);