For the recent Div 4 contest problem E (Romantic Glasses)

https://mirror.codeforces.com/contest/1915/problem/E

https://mirror.codeforces.com/contest/1915/submission/239539914 is TLE uses dict

whereas

https://mirror.codeforces.com/contest/1915/submission/239522644 passes uses set

I'm not sure why there would be this much difference in execution time.

Thanks for your time.