Display possible combinations of string

Question

I am trying to take a string and display the possible combinations of it (in PHP), but while saying in order of each word. For example: \"how are you\" would return (an arra

Answer 1

I know this is a very old post, but the other answer isn't very flexible, so I thought I would bring a new answer in.

Explanation

So you are looking for all combinations which would be:

(2ⁿ) - 1

Which in your specific example would be:

(2³) - 1 = (8) - 1 = 7

So how do I get all combinations now? We loop through all our combinations, which we already have(Starting off with one combination, an "empty combination" ($results = [[]];)), and for each combination we go through our next word from the array and combine each combination with each new word to a new combination.

Example

Array with the words/numbers (Empty array is '[]'):
[1, 2, 3]

                               //↓new combinations for the next iteration
                               │
iteration 0:

    Combinations:
                  - []         │  -> []
                                  │
iteration 1:        ┌─────────────┤
                    │             │
    Combinations:   v             v
                  - []    + 1  │  -> [1]    
                                  │
iteration 2:        ┌─────────────┤
                    │             │
    Combinations:   v             v
                  - []    + 2  │  -> [2]
                  - [1]   + 2  │  -> [1,2]    
                                  │
iteration 3:        ┌─────────────┤
                    │             │
    Combinations:   v             v
                  - []    + 3  │  -> [3]
                  - [1]   + 3  │  -> [1,3]
                  - [2]   + 3  │  -> [2,3]         
                  - [1,2] + 3  │  -> [1,2,3]    
                               //^ All combinations here

So as you can see there is always: (2^n)-1 combinations in total. Also from this method there is an empty array left in the combination array, so before I return the array I just use array_filter() to remove all empty arrays and array_values() to reindex the entire array.

Code

 $element) {
            foreach ($results as $combination)
                $results[] =  $combination + [$k => $element];
        }

        //return filtered array
        return array_values(array_filter($results));

    }


    $arr = getCombinations(explode(" ", $str));

    foreach($arr as $v)
        echo implode(" ", $v) . "
";


?>

output:

how
are
how are
you
how you
are you
how are you