Generation of a unique combination by means of php?

Question

PHP

It is required to generate a unique combination. The combination consists of 16 digits
, each digit is in the range from 1 to 10.
Example: 1 9 2 6 10 9 3 7 1 3 9 10 3 6 10 2
Played with mt_srand() and other things. I haven't been able to find an ideal solution.
10^16 shows a very large number of possible combinations (if I remember the school computer science course). But when there are 16k duplicates for 50k, this is nothing. In the most stupid random, it turned out to be 10k - 200 duplicates.
The field with the combination has a unique index in the base, so I really don't want to skip combinations. Or at least reduce the number of duplicates to a minimum.
What are the generation options?

Answer 1

You must understand that random values ​​are random, they are repeated and cannot be generated for unique fields. Use autoincrement.

Answer 2

Obviously, pseudo-random numbers are not the best way to get a unique key.
But essentially this is the code:

function getRandSeq($seq_len) {
    $result = array();
    for ($i=1; $i<=$seq_len; $i++)
        $result[] = rand(1, 10);
    return implode(" ", $result);    
}
function getMtRandSeq($seq_len) {
    $result = array();
    for ($i=1; $i<=$seq_len; $i++)
        $result[] = mt_rand(1, 10);
    return implode(" ", $result);    
}
//
$total = 50000;
$seq_arr1 = array();
$seq_arr2 = array();
$dbl_count1 = 0;
$dbl_count2 = 0;
for ($t=1; $t<=$total; $t++) {
    $seq1 = getRandSeq(16);
    $seq2 = getMtRandSeq(16);    
    if (in_array($seq1, $seq_arr1))
        $dbl_count1++;
    if (in_array($seq2, $seq_arr2))
        $dbl_count2++;           
    $seq_arr1[] = $seq1;
    $seq_arr2[] = $seq2;    
}
echo $dbl_count1."/".$dbl_count2."/".$total;

Returned to me:
47952/0/50000
I.e. for 50k generations, rand gives a bunch of repetitions, but mt_rand is 0.

Answer 3

Is it possible to use the UUID function ?
True, the format may not be suitable.
Option 2, not productive, generating a number in a cycle with requests for uniqueness to the database, not unique, so we generate a new one.

Answer 4

Try generating numbers from 10^15 to 10^16-1 instead of combinations.

Answer 5

entropy in Unixes is in /dev/random
, however, its quantity is limited, you have to wait
or use /dev/urandom
you need to get not 16 numbers from 1 to 10, but one sequence of about 50 bits long (that is, it will turn out 50-digit number with base 2, it can be converted to a number with base 10)