/*
Enter your query here.
 hacker_id, name, and the total number
*/

with results as 
(
select 
h.hacker_id 
,h.name 
,count(distinct c.challenge_id) challenges
,rank () over(order by count(distinct c.challenge_id) desc)   as rank_order
from hackers h 
left join challenges c
    on h.hacker_id = c.hacker_id
group by 1,2
order by count(distinct c.challenge_id) desc, hacker_id asc
)

,repeated_ranks as 
(select 
 rank_order
 ,count(*) as counter
from results 
where rank_order <> 1
 group by 1
having count(*)>1
)

select 
r.hacker_id
,r.name
,r.challenges
from results r
left join repeated_ranks rr
 on r.rank_order = rr.rank_order
 where 1=1
 and rr.counter is null