(: Helper functions :)

declare function local:distinct($a) {
        $a[index-of($a,.)[1]]
};

(: Group 1 :)

(: ** which building has the most courses? :)

let $list := (
    let $buildings := (
        for $courses in //course
            return $courses//building)
    for $building in distinct-values($buildings)
        return $building)
for $b in $list
    return <ans>{$b}, {count(//building[text() eq $b])}</ans>

(:Group 2 :)

(: ** which instructor in a building has the earliest courses :)

let $all = //courses
let $blist = distinct-values(//courses//building)
for $b1 in $blist
    let $timelist = (for $b2 in $all
    where $b1 = $b2//building
    let $t = $b2//time/start_time[matches(. , 'AM')]
    order by $t
    return $t)
let $instr = $timelist[1]/ancestor::course/instructor
return $instr

(: Group 5 :)

(: *  list all courses that start before 10am :)

for $c in //course
where $c//start_time < "10:00AM" and substring($c//start_time, 6, 2) = "AM"
return <r> {$c} </r>

(: *  name all  instructors that teach at least three courses :)

let $i := local:distinct(//instructor)
for $t in $i
where count(//course[./instructor=$t]) >= 3
return <r> {$t} </r>


(: Group 6 :)
(: **  Which building has the most rooms? :)

let $total:=(
    for $b in local:distinct(//building)
        let $c := //place[./building = $b]
        let $count := count($c/room)
        return <bg>
                <bl>{$b/text()}</bl>
                <count>{$count}</count>
               </bg>)
let $maxcount := max($total//count)
return $total[count = $maxcount]/bl


(: **  what courses are taught in a given room in a given building and when?
   **  (you can pick a room/building that s interesting). :)

for $cs in //course[.//building/text()='PHYSIC' and .//room/text()='134']
    return <course>{$cs//title,$cs//time}</course>