Miky - 3 months ago 22

PHP Question

php:

Given a list of non repetitive strings, like

`$strings=array("asd","qwerty","123");// or more`

I'd like to get all non repetitive combinations (no matter the order) like

`asd`

asd qwerty

asd 123

asd qwerty 123

qwerty

qwerty 123

123

I'm looking for the most efficient algorithm possible and in a single function

Answer

The main idea is that number of combinations (if all strings are different) is n^2 - 1, where n = count of strings. Thus we can use binary representation of i-th combination to build our unique combination.

In code it looks like this:

```
$someArray = ['abc', 'def', 'foo', 'bar'];
$combinations = pow(2, count($someArray)) - 1;
$result = [];
for ($i = 0; $i < $combinations; $i++) {
$result[$i] = [];
for ($j = 0; $j < count($someArray); $j++) {
// here we check if j-th bit of i is equal to 1
if (($i >> $j) & 1 == 1) {
$result[$i][] = $someArray[$j];
}
}
}
```