基于字符集的固定长度的所有字符串组合

Question

I'm looking to create a function that will return every possible string within a given string length, using a charset.

As an example, a charset of "abc", and a length of 2 should allow for 9 (3 ^ 2) unique combinations:

aa, ab, ac, ba, bb, bc, ca, cb, cc

(List constructed manually)

What method could be used to create such a function?

Answer 1

As always, there are multiple ways to solve what you ask for, this is only one way, using one counter per character in the output string:

$c = "abc"; // charset
$l = 2; // string length

for($t='',$cl=strlen($c),$s=array_fill(0,$l,0),$i=pow($cl,$l);$a=0,$i--;) {
    for($t&&$t.=', ';$a<$l;$t.=$c[$s[$a++]]);
    for(;$a--&&++$s[$a]==$cl;$s[$a]=0);
};

echo $t; // the string you asked for.

aa, ab, ac, ba, bb, bc, ca, cb, cc

One main loop, one loop to build the string and one loop for counting up.

I can imagine this should work with getting modulos per each position of the output string as well.