Pseudo random string

Question

I need generate codes from this letters

$a = array(
 'B','C','D','F','G','H','J','K','L','M','N','O',
 'P','Q','R','S','T','V','W','X','Y','Z','1','2',
 '3','4','5','6','7','8','9','0'
);

But there are 2 conditions: every code must be unique and contains 10 letters. I don't want to get random because is unefficient. Instead, I want go for every letter e.g.:

1. BBBBBBBBBB
2. BBBBBBBBBC
3. BBBBBBBBBD

and so on.. Any ideas?

• lonesomeday: Why not just use something like uniqid? I can guarantee that that will be far more efficient than building the string yourself.
• ariel: I need to generate 1,6mln codes and save them to data base. How to use uniqid?

Answer 1

I think that what you actually want is a list of sequential numbers (therefore not random at all) with a rather unconvetional base system. So BBBBBBBBB is 0, while BBBBBBBC is 1. This isn't hard to do, but obviously you have to code it yourself. Something like this might work:

function generate($num) {
 $num = base_convert($num, 10, 32); // convert the number to base 32
 $num = str_pad($num, 10, "0", STR_PAD_LEFT); // pad it with zeros to the left
 $num = str_replace(array(
 '0','1','2','3','4','5','6','7','8','9','a','b',
 'c','d','e','f','g','h','i','j','k','l','m','n',
 'o','p','q','r','s','t','u','v'
 ), array(
 'B','C','D','F','G','H','J','K','L','M','N','O',
 'P','Q','R','S','T','V','W','X','Y','Z','1','2',
 '3','4','5','6','7','8','9','0'
 ), $num); // replace the normal characters with your custom array
 echo $num, "\n";
}
for ($i = 0; $i < 10; $i++) generate($i);

Obviously you could change the 10 in the for statement to whatever you liked, and insert into a database rather than echoing. Obviously 1.6m records would take some time to generate.

The above code gives the following output:

BBBBBBBBBB
BBBBBBBBBC
BBBBBBBBBD
BBBBBBBBBF
BBBBBBBBBG
BBBBBBBBBH
BBBBBBBBBJ
BBBBBBBBBK
BBBBBBBBBL
BBBBBBBBBM

• Peter: Clever solution, but quite slow
• lonesomeday: @PeterSzymkowski Well yes. But let's face it: if speed is the objective, the solution is to use plain old numbers.
• DaveRandom: +1 for this, definitely the most simplistic answer that gets the job done. One thing to consider (and this applies to any approach) is that you would need to store this in the database on the fly, as filling an array with the generated values will consume insane amounts of memory.
• DaveRandom: Incredibly @PeterSzymkowski's solution is more than 6 times faster on my dev machine, though.

Answer 2

<?php
$length = 3;
$letters = str_split("ABC"); // define your dictionary here
$index = array_fill(0, $length, 0);
$key = $length - 1;
while(true) { 
 $code = "";
 for($i=0;$i<$length;$i++) { 
 $code .= $letters[$index[$i]]; 
 }
 echo $code ."<br/>"; // output code
 $index[$key]++;
 while(!isset($letters[$index[$key]])) {
 $index[$key] = 0;
 $key--;
 if($key < 0) {
 break 2;
 } 
 $index[$key]++;
 } 
 $key = $length - 1; 
}

Example:

• http://codepad.org/9XO9pKJK

• Sergey: Good solution, but replace: $index = Array(); for($i=0;$i<$length;$i++) { $index[$i] = 0; } by $index = array_fill(0, $length, 0); -
• lonesomeday: For what it's worth, here is a codepad with the format and dictionary requested by the OP. This is indeed significantly (5 to 10 times) faster than my solution, so a big +1.

Answer 3

<?php
$a = array(
 'B','C','D','F','G','H','J','K','L','M','N','O',
 'P','Q','R','S','T','V','W','X','Y','Z','1','2',
 '3','4','5','6','7','8','9','0'
);
function key_increment (&$symbols, $position = null) 
{
 global $a;
 if ($position === null) $position = count($symbols) - 1;
 if ($position == -1) return;
 $index = $symbols[$position];
 $index ++;
 if (!isset($a[$index])) {
 $v = 0;
 key_increment ($symbols, $position-1);
 }
 $symbols[$position] = $value;
}
function generate($length, $total) 
{
 global $a;
 $symbols = array_fill(0, $length, 0);
 for ($i = 0; $i < $total; $i ++) {
 $code = '';
 foreach ($symbols as $index) {
 $code .= $a[$index];
 }
 echo $code;
 echo '<br />';
 key_increment($symbols);
 }
}
generate(3, 100);

• Sergey: @PeterSzymkowski, yes, but it's cleary show how it must work. lonesomeday's questions is prefer
• lonesomeday: This code evidently works, but it's rather hard to follow. Do you think you could use descriptive variable names, rather than $s, $v, etc.?

Answer 4

It's probably best that you just use uniqid, especially seeing as you said you'll be generating 1.6 million codes . If you're concerned about the case, just use strtoupper()

echo strtoupper(uniqid());

Generating all of these and inserting them is going to take a fair bit of time.