PHP求给定数组的组合

1、求给定数组的组合

如array('a', 'b', 'c')

结果为

a

b

c

a b

a c

b c

function combination($arr){
    if(empty($arr)){
        return false;
    }
    $count = count($arr);
    for($i=1; $i<$count; $i++){
        combinationResult($arr, 0, $count, $i);
    }
}
function combinationResult($arr, $begin, $end, $number){
    static $result = array();
    if($number == 0){
        $count = count($result);
        for($i=0; $i<$count; $i++){
            echo $result[$i] . ' ';  
        }
        echo '
';
        return true;
    }
    if($begin == $end){
        return false;
    }
    array_push($result, $arr[$begin]);
    combinationResult($arr, $begin+1, $end, $number-1);
    array_pop($result);
    combinationResult($arr, $begin+1, $end, $number);
}
$arr = array('a', 'b', 'c', 'd');
combination($arr);