| № | Пользователь | Рейтинг |
|---|---|---|
| 1 | tourist | 3880 |
| 2 | jiangly | 3669 |
| 3 | ecnerwala | 3654 |
| 4 | Benq | 3627 |
| 5 | orzdevinwang | 3612 |
| 6 | Geothermal | 3569 |
| 6 | cnnfls_csy | 3569 |
| 8 | jqdai0815 | 3532 |
| 9 | Radewoosh | 3522 |
| 10 | gyh20 | 3447 |
| Страны | Города | Организации | Всё → |
| № | Пользователь | Вклад |
|---|---|---|
| 1 | awoo | 161 |
| 2 | maomao90 | 160 |
| 3 | adamant | 156 |
| 4 | maroonrk | 153 |
| 5 | -is-this-fft- | 148 |
| 5 | atcoder_official | 148 |
| 5 | SecondThread | 148 |
| 8 | Petr | 147 |
| 9 | nor | 144 |
| 9 | TheScrasse | 144 |
There is a string with length n ≤ 104.
Let us denote fi as number of occurrences of the i'th unique sub sequence.
We need to calculate 
. Sub sequence does not have to be consective.
I have no idea about the solution so far. So any help would be appreciated.
Here is the source of the problem : link
How to count amount of different subsequences of a string?..
Hint: For each distinct sub sequence count it when its lexicographically minimal by index values.
Some magic: http://www.everfall.com/paste/id.php?tuo8fxsbhlx0.
The main idea is that desired sum may be obtained in the following way: let's iterate over all pairs of subsequences in the string
Sand doans += 1iff they are equal.