Editorial for GlobeX Cup '18 J5 - Errands
Remember to use this editorial only when stuck, and not to copy-paste code from it. Please be respectful to the problem author and editorialist.
Submitting an official solution before solving the problem yourself is a bannable offence.
Submitting an official solution before solving the problem yourself is a bannable offence.
Author:
For the first subtask, it suffices to BFS from to
and from
to
for each query. Then, to get the answer to the queries, we can just sum the distance from
to
and
to
.
For this subtask, if is unreachable through either the first or second BFS, print
This is a scam!
.
Time Complexity:
For the second subtask, note that we can instead BFS from to
and
instead of the other way around. With that information in mind, we can also note that
stays constant throughout the queries, so we only need to run one BFS at the beginning from
to every other node.
Now, all we have to do for each query is sum and
.
Note that if either or
are unreachable, print
This is a scam!
.
Time Complexity:
Comments