gistfile1.php

<?php
function factorial($n) {
    if($n==0) return 1;
    $t=$n--;
    while ($n > 0) {
        $t*=($n--);
    }
    return $t;
}

function combinations($n) {
    $t=0;
    //echo $t;
    $nFactorial = factorial($n);
    for($r=1; $r<=$n; $r++) {
        //echo " + (".$nFactorial/factorial($n-$r).") ";
        $t += $nFactorial/factorial($n-$r);
    }
    return $t;
}

for($i=1; $i<10; $i++) {
    echo "$i => ";
    echo number_format(combinations($i));
    echo PHP_EOL;
}

function applyBlacklist($blacklistPhrase, $searchWords) {
    // first sort the terms for skippin gmatches - think selection sort.
    sort($blacklistPhrase);
    sort($searchWords);

    foreach($blacklistPhrase as $blacklistword) {
        if(!in_array($blacklistword, $searchWords)) {
            return false;
        }
    }

    // Think in terms of PHP arrays - one liner!
    return count($blacklistPhrase) == count (array_intersect($blacklistPhrase, $searchWords));

    return true;
}


$tests = array (
    array(
        "name" => "direct match",
        "blacklist" => "a b c",
        "search" => "a b c",
        "result" => true,
    ),
    array(
        "name" => "search out of order.  Partial search match",
        "blacklist" => "a b",
        "search" => "c b a",
        "result" => true,
    ),
    array(
        "name" => "complete mismatch",
        "blacklist" => "a b c",
        "search" => " d e f",
        "result" => false,
    ),
    array(
        "name" => "partial match - incomplete",
        "blacklist" => "a b c",
        "search" => "a d e f",
        "result" => false,
    ),

);

foreach($tests as $case) {
    $blacklist = explode(' ', $case['blacklist']);
    $search = explode(' ', $case['search']);
    $result = applyBlacklist($blacklist, $search);
    echo $case['name'] . "\t ==> ";
    var_dump($result == $case['result']);
}