How to decompose a number in PHP?

Question

PHP

The essence of the idea:
Let's say I have ip 192.168.0.1
The sum of all numbers 28 (1 + 9 +2 +1 + 6 + 8 + 0 + 1 = 28)
How can I get all possible variations of IP addresses from number 28 (zero incl. h.)?

Thank you all in advance!

Answer 1

You can immediately get the desired IP addresses without going through all the options - if you go not from numbers, but from the sum of the digits of each number.
As a result, the script in which echo was replaced by ++$count ran for less than 14 seconds and counted 112279695 addresses.

$tbl = array_fill(0, 20, []);
for ($i = 0; $i < 256; ++$i) { $tbl[intdiv($i, 100) + intdiv($i, 10) % 10 + $i % 10][] = $i; }
for ($i = 0; $i <= 19; ++$i) {
    for ($j = 0; $j <= min(19, 28 - $i); ++$j) {
        for ($k = max(0, 28 - 19 - $i - $j); $k <= min(19, 28 - $i - $j); ++$k) {
            foreach($tbl[$i] as $v1) {
                foreach($tbl[$j] as $v2) {
                    foreach($tbl[$k] as $v3) {
                        foreach($tbl[28 - $i - $j - $k] as $v4) {
                            echo $v1, '.', $v2, '.', $v3, '.', $v4, "\n";
                        }
                    }
                }
            }
        }
    }
}

The sum of the digits of a number in the range 0..255 has a range of values ​​from 0 (0) to 19 (199).
$tbl - an array of lists of numbers in the range 0..255 that have the same sum of digits.

Answer 2

192.168.0.1
This is an alphabet from 0 to 255.
Permutations are an anagram for a 4-letter word.
It is possible to hash through prime numbers :

0 -> 2
1 -> 3
2 -> 5
3 -> 7
...
255 -> ...

Then multiply the simple 4th numbers (to the right of the arrow) corresponding to one of the 4 values ​​(from 0 to 255: ABCD) in the ip address: the result for any permutation will always be the same.