Hello Codeforces, yesterday I have submitted various solutions for problem C. Although I have estimated my time and memory complexity to be O(n log n) I was surprised to see that it gave time limit exceeded, can you help me? 188111812
# | User | Rating |
---|---|---|
1 | tourist | 3803 |
2 | jiangly | 3707 |
3 | Benq | 3627 |
4 | ecnerwala | 3584 |
5 | orzdevinwang | 3573 |
6 | Geothermal | 3569 |
6 | cnnfls_csy | 3569 |
8 | Radewoosh | 3542 |
9 | jqdai0815 | 3532 |
10 | gyh20 | 3447 |
# | User | Contrib. |
---|---|---|
1 | awoo | 163 |
1 | maomao90 | 163 |
3 | adamant | 161 |
4 | maroonrk | 152 |
5 | -is-this-fft- | 151 |
6 | nor | 150 |
7 | atcoder_official | 147 |
7 | SecondThread | 147 |
9 | TheScrasse | 146 |
10 | Petr | 145 |
Hello Codeforces, yesterday I have submitted various solutions for problem C. Although I have estimated my time and memory complexity to be O(n log n) I was surprised to see that it gave time limit exceeded, can you help me? 188111812
Name |
---|
std upper bound is linear on sets, use set::upper_bound instead
Oh wow! That got AC. Why does this happen? Are there any other functions I need to be cautious when using? Thank you very much for your reply.
lower_bound()
:D
You called a general function
std::upper_bound
. The way this function works is: if it is called on random access iterator, such asstd::vector<int>::iterator
, a binary search is performed, achieving $$$O(\log n)$$$ (since it is possible to access any position in constant time). Otherwise, if the iterator is not random access (such asstd::set<int>::iterator
),std::upper_bould
can't do any better than to just advance the iterator linearly to find the answer.On the other hand,
std::set<int>::upper_boupd
has access to the inner workings of set, which is a binary search tree, so it can go up and down the tree in a smart way to get the answer in $$$O(\log n)$$$.Thank you so much!
downvoted. upper blund is not the problem. optimization is the issue.
please get your facts straight. The problem was clearly upper_bound