PHP Find All (somewhat) Unique Combinations of an Array

Question

I\'ve been looking at PHP array permutation / combination questions all day.. and still can\'t figure it out :/

If I have an array like:

20 //key bei         


        

Answer 1

Had the same problem and found a different and bitwise, faster solution:

function bitprint($u) {
    $s = array();
    for ($n=0; $u; $n++, $u >>= 1){
        if ($u&1){
            $s [] = $n;
        }
    }
    return $s;
}
function bitcount($u) {
    for ($n=0; $u; $n++, $u = $u&($u-1));
    return $n;
}
function comb($c,$n) {
    $s = array();
    for ($u=0; $u<1<<$n; $u++){
        if (bitcount($u) == $c){
            $s [] = bitprint($u);
        }
    }
    return $s;
}

This one generates all size m combinations of the integers from 0 to n-1, so for example m = 2, n = 3 and calling comb(2, 3) will produce:

0 1
0 2
1 2

It gives you index positions, so it's easy to point to array elements by index.

Edit: Fails with input comb(30, 5). Have no idea why, anyone any idea?