Question

I am trying to write a function that will replace characters in a string with their HTML entity encoded equivalent.

I want it to be able to go through all the possible combinations for the given string, for example:

• go one-by-one
• then combo i.e.. 2 at a time, then three at a time, till you get length at a time
• then start in combo split, i.e.. first and last, then first and second to last
• then first and last two, fist and second/third last

So for the characters “abcd” it would return:

abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd
abcd

etc………. so on and so forth till there are no other combinations

Any ideas, or has anyone seen a function somewhere I could modify for this purpose?

Answer 1

loop from 0 to 2^length – 1. On each step, if Nth bit of the loop counter is 1, encode the Nth character

$str = 'abcd';

$len = strlen($str);

for($i = 0; $i < 1 << $len; $i++) {
    $p = '';
    for($j = 0; $j < $len; $j++)
        $p .= ($i & 1 << $j) ? '&#' . ord($str[$j]) . ';' : $str[$j];
    echo $p, "\n";
}