I was trying to submit this -> Remove Max Number of Edges to Keep Graph Fully Traversable question.
but I got TLE because of sort using rbegin

sort( edges.rbegin(), edges.rend())

but after change with comparator funtction code got accepted.

sort(edges.begin(), edges.end(), [&](vector <int> &a, vector <int> &b){
            return a[0] > b[0];
        });

Submission Using rbegin

Submission Using comparator

I tried to run this in local and got similar performance but when I used some different build command I got 2x time difference.

Build command:

g++ a.cpp

g++ -std=c++17 -Wshadow -Wall -fsanitize=address -fsanitize=undefined -D_GLIBCXX_DEBUG -DLOCAL a.cpp

Following code I used for bench-marking.

Bench-marking code

Can anyone explain why this time difference happening?
Will this happen in code-forces also?