In the last educational round, my below solution for the problem 2004D - Colored Portals got TLE.

TLE solution: 276676175

After the contest, I submitted the solution with only one line of change in code and it got AC.

AC solution: 276725505

The only difference between both the codes is:

In the TLE solution:

for (auto x : mp)

And in the AC solution:

for (auto x = mp.begin(); x != mp.end(); x++)

Anyone, please help me to find out the time complexity of each statement. And why this first one gives TLE?

Which statement should be preferred to avoid this type of situation?