I have usually used map.insert() to put a value in the map and known that this would update automatically if there is already the existing key value.
But I realized that this does not overwrite the overlapping value.
https://www.acmicpc.net/problem/15461
This was a tough problem but I managed to come up with an idea and submitted the solution.
But it kept saying that it is wrong.
After several hours of debugging, I found that the problem was that in the map, values which should be deleted have not been eliminated and new values were added again and again.
idAndValue.insert(pair<int, int> (cow, after));
Originally the algorithm should change the value corresponding to “cow id” into after continuously, but instead, the size of map kept growing.
So I searched about it, and the reason is that map.insert() itself put a value at the beginning but does not update it into new value.
Eventually, I found that map[key] = value adds a new value if there is no key and updates existing value into value if there is key.
It’s so simple…
idAndValue[cow] = after;
I got the correct answer with a shorter and clean code.