Yesterday, I have participated in codeforces round 773.
Was able to solve the first three questions during the contest, but my B and C submission got TLE on System Cases, do you know why? Just because I have used unordered_map instead of map.
I think, this is practical example to examine the diff btw unordered_map and map.
The same code with the same logic gives TLE, when using UMAP but got accepted, when using MAP.
1642B - Power Walking Submission with UMAP: submission:147440230
1642C - Great Sequence Submission with UMAP: submission:147426920
1642B - Power Walking Submission with MAP: submission:147497381
1642C - Great Sequence Submission with MAP: submission:147497320
One of my codeforces friends also told me about this, with a very good resource attached, you can check it.
Any suggestions are welcomed!