Hi Everyone ! I am not able to understand how to break this problem into subproblems ?
Can someone help please ? Here is the problem link : Problem
Изменения рейтингов за последние раунды временно удалены. Скоро они будут возвращены.
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| № | Пользователь | Рейтинг |
|---|---|---|
| 1 | jiangly | 3640 |
| 2 | Benq | 3593 |
| 3 | tourist | 3572 |
| 4 | orzdevinwang | 3561 |
| 5 | cnnfls_csy | 3539 |
| 6 | ecnerwala | 3534 |
| 7 | Radewoosh | 3532 |
| 8 | gyh20 | 3447 |
| 9 | Rebelz | 3409 |
| 10 | Geothermal | 3408 |
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| 1 | maomao90 | 174 |
| 2 | awoo | 164 |
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| 4 | TheScrasse | 159 |
| 5 | nor | 158 |
| 6 | maroonrk | 156 |
| 7 | -is-this-fft- | 151 |
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| 10 | pajenegod | 145 |
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Just Bumping it . In case someone wanna help .
Think about the last row of the tower. You can either have both cells as a part of the same block, or both cells as parts of different blocks. Let's call towers of the first kind type-1 towers, and the towers of the second kind type-2 towers.
Let's call $$$a_n$$$ be the number of type-1 towers and $$$b_n$$$ be the number of type-2 towers.
For computing $$$a_n$$$, look at what remains when you remove the last row from the tower. Corresponding to a type-1 tower of height $$$n - 1$$$, there will be two such towers, and corresponding to a type-2 tower of height $$$n - 1$$$, there will be one such tower, so $$$a_n = 2a_{n - 1} + b_{n - 1}$$$. In a similar manner you have $$$b_n = 4b_{n - 1} + a_{n - 1}$$$.
Then you can either precompute the answers to all possible queries, or use matrix exponentiation to solve the recurrence. The answer is $$$a_n + b_n$$$.
Thanks a lot .
When computing bn, you consider the last row to build the type-2 tower right ? But I don't understand why it can be 4 * b(n-1) + a(n — 1) sir. Thanks you if you can explain to me!!
Because the lower n-1 level can have either one a[n-1] and one b[n-1] because of solid border, or 2 b[n-1] breaking any of the borders, and b[n-1] when breaking both the borders. Here border is the line between the nth and (n-1)th row.
can someone tell me the rating of this problem acc to codeforces