Kattis Challenge - Recount - count who has the most votes in a list of names
There are 2 important performance issues here:


find(...) in a vector performs a linear search, \$O(n)\$. You would do better by using a hash map instead, that would allow constant-time search, \$O(1)\$.
Sorting the candidates by vote count is unnecessary to find the ones with the maximum count. Sorting is an \$O(n \log n)\$ operation. You can find the maximum with a linear search, \$O(n)\$, and in a second linear pass you could verify if a run-off is needed. (You could as well make this part of step 1 and do it in a single pass, but that wouldn't change the order of complexity of the algorithm.)


Lastly, a minor thing, but the implementation will fail if there are less than two candidates :-)