A simple, low-memory footprint function to generate all string combinations from a series of characters.
PHP 7.4+ is required.
composer require bentools/string-combinations
I want to get all combinations with the letters a
, b
, c
.
require_once __DIR__ . '/vendor/autoload.php';
use function BenTools\StringCombinations\string_combinations;
foreach (string_combinations('abc') as $combination) { // Can also be string_combinations(['a', 'b', 'c'])
echo $combination . PHP_EOL;
}
Output:
a
b
c
aa
ab
ac
ba
bb
bc
ca
cb
cc
aaa
aab
aac
aba
abb
abc
aca
acb
acc
baa
bab
bac
bba
bbb
bbc
bca
bcb
bcc
caa
cab
cac
cba
cbb
cbc
cca
ccb
ccc
Array output
It will dump all combinations into an array.
var_dump(string_combinations('abc')->asArray());
Count combinations
It will return the number of possible combinations.
var_dump(count(string_combinations('abc'))); // 39
Specifying min length, max length
foreach (string_combinations('abc', $min = 2, $max = 2) as $combination) {
echo $combination . PHP_EOL;
}
Output:
aa
ab
ac
ba
bb
bc
ca
cb
cc
Using an array as first argument, and a separator
foreach (string_combinations(['woof', 'meow', 'roar'], 2, 3, '-') as $combination) {
echo $combination . PHP_EOL;
}
Output:
woof-woof
woof-meow
woof-roar
meow-woof
meow-meow
meow-roar
roar-woof
roar-meow
roar-roar
woof-woof-woof
woof-woof-meow
woof-woof-roar
woof-meow-woof
woof-meow-meow
woof-meow-roar
woof-roar-woof
woof-roar-meow
woof-roar-roar
meow-woof-woof
meow-woof-meow
meow-woof-roar
meow-meow-woof
meow-meow-meow
meow-meow-roar
meow-roar-woof
meow-roar-meow
meow-roar-roar
roar-woof-woof
roar-woof-meow
roar-woof-roar
roar-meow-woof
roar-meow-meow
roar-meow-roar
roar-roar-woof
roar-roar-meow
roar-roar-roar
No duplicates
You can avoid generating stings having the same letter more than once with the withoutDuplicates()
method:
$combinations = string_combinations('abc');
var_dump(count($combinations)); // 39
print_r($combinations->asArray());
Array ( [0] => a [1] => b [2] => c [3] => aa [4] => ab [5] => ac [6] => ba [7] => bb [8] => bc [9] => ca [10] => cb [11] => cc [12] => aaa [13] => aab [14] => aac [15] => aba [16] => abb [17] => abc [18] => aca [19] => acb [20] => acc [21] => baa [22] => bab [23] => bac [24] => bba [25] => bbb [26] => bbc [27] => bca [28] => bcb [29] => bcc [30] => caa [31] => cab [32] => cac [33] => cba [34] => cbb [35] => cbc [36] => cca [37] => ccb [38] => ccc )
$combinations = $combinations->withoutDuplicates();
var_dump(count($combinations)); // 15
print_r($combinations->asArray());
Array ( [0] => a [1] => b [2] => c [3] => ab [4] => ac [5] => ba [6] => bc [7] => ca [8] => cb [9] => abc [10] => acb [11] => bac [12] => bca [13] => cab [14] => cba )
Because it uses Generators to generate all possible combinations, you can iterate over thousands of possibilities without losing a single MB.
This has been executed on my Core i7 personnal computer with 8GB RAM:
require_once __DIR__ . '/vendor/autoload.php';
use function BenTools\StringCombinations\string_combinations;
$start = microtime(true);
$combinations = string_combinations('abcd1234');
foreach ($combinations as $c => $combination) {
continue;
}
$end = microtime(true);
printf(
'Generated %d combinations in %ss - Memory usage: %sMB / Peak usage: %sMB' . PHP_EOL,
++$c,
round($end - $start, 3),
round(memory_get_usage(true) / 1024 / 1024),
round(memory_get_peak_usage(true) / 1024 / 1024)
);
Output:
Generated 19173960 combinations in 5.579s - Memory usage: 2MB / Peak usage: 2MB
./vendor/bin/phpunit