Increment through A-Za-z0-9 in expanding string with PHP

I'm trying to generate strings in PHP with a group of valid characters, cycling through them and appending an extra character on the end of the string, until maximum length is reached. For example, desired output:

a,b,c,d开发者_如何学C,e,f,aa,ab,ac,ad,ae,af,ba,bb,bc,bd,be,bf,ca,cb..etc

This is my PHP function so far:

<?php

$chars = Array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
        'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','X','Y','Z',
        '1','2','3','4','5','6','7','8','9','0');
$maxlen = 10;

$input = $chars[0];
while (1):
    echo buildInput($maxlen, $chars, $input) . "\n";
endwhile;

function buildInput($maxlen, $chars, $previous)
{
        if (array_search(substr($previous, -1), $chars) == sizeof($chars) - 1):
                // end of input cycle reached, add another character
                $previous = $previous . $chars[0];
        endif;

        if (strlen($previous) > $maxlen):
                die('Max length reached');
        endif;

        // Remove last character, and append incremented char
        $input = substr($previous, 0, -1);
        $input = $input . $chars[array_search(substr($previous, -1), $chars)+1];

        return $input;
}
?>

It only increments the last character of the string which gets to 0, then appends 'a' and starts over but without trying all the other possible permutations.

Could someone help me with a better method?

Is this the kind of thing you want?

<?php
    $chars = array('a','b','c');
    $max_length = 3;

    function build($base_arr, $ctr) {
        global $chars;
        global $max_length;

        $combos = array();

        foreach ($base_arr as $base) {
            foreach ($chars as $char) {
                echo $base, $char, '<br />';
                $combos[] = $base.$char;
            }
        }

        if ($ctr < $max_length) {
            build($combos, $ctr + 1);
        }
    }

    foreach ($chars as $char) {
        echo $char, '<br />';
    }

    build($chars, 2);
?>

It'll give you: a, b, c, aa, ab, ac, ba, bb, bc, ca, cb, cc, ..., bcc, caa, cab, cac, cba, cbb, cbc, cca, ccb, ccc.

Your array is so large, though, that using this method on it would take up way too much memory to work. Out of 62 characters (A-Z, a-z, 0-9), the number of possible 10-character permutations is 8.4 x 10^17; so hopefully, you'll be able to find a more efficient method or figure out a way to get the result you want without having to cycle through such a large array. I hope you find what you're looking for!

If you limit yourself to 0-9,a-z (only lower case), then you could use base_convert for this and do it in one line:

for($i = 0; $i < 1000; $i++) echo base_convert($i, 10, 36) . '<br/>';

Here's a demo.

This will print 200 letters: a,b,c,d,...,aa,...,cq

The buildString function will build our string from the least significant number (right) to the most significant (left). By performing a modulus division, you will find the array position of the next character. Add this character to the front of your string, and divide your number by the size of your array (which is the base number in your character based number system), ignoring the rest.

To explain the method using our normal 10-based number system and the input of 123, you would simply pick the last digit, 3, divide the input by 10, pick the last digit 2, divide the input by 10, pick the last digit 1, divide the input by 10. The input is now 0 and your output is ready...

$chars = array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q'
    ,'r','s','t','u','v','w','x','y','z','A','B','C','D','E','F','G','H','I','J'
    ,'K','L','M','N','O','P','Q','R','S','T','U','V','X','Y','Z','1','2','3','4'
    ,'5','6','7','8','9','0');
$numChars = count($chars);

// Output numbers from 1 to 200 (a to cq)
for($i = 1; $i <= 200; $i++) {
    echo buildString($i).'<br>';
}

// Will also work fine for large numbers - output "dxSA"
echo buildString(1000000).'<br>';

function buildString($int) {
    global $chars;
    global $numChars;

    $output = '';
    while($int) {
        $output = $chars[($int-1) % $numChars] . $output;
        $int = floor(($int-1) / $numChars);
    }

    return $output;
}

If you have access to gmp extension and PHP 5.3.2+ this will work for the charset you specified:

$result = strtr(
    gmp_strval(gmp_init($i, 10), 62),
    '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz',
    'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
);