In this problem http://www.spoj.com/problems/PLD/ , what is the best way to use rabin_karp?
To precalculate hashes,or add-delete numbers? Cause I am stuck at this 4 hours now... :(
# | User | Rating |
---|---|---|
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 |
# | User | Contrib. |
---|---|---|
1 | awoo | 161 |
2 | maomao90 | 160 |
3 | adamant | 156 |
4 | maroonrk | 153 |
5 | atcoder_official | 148 |
5 | -is-this-fft- | 148 |
5 | SecondThread | 148 |
8 | Petr | 147 |
9 | nor | 144 |
10 | TheScrasse | 142 |
In this problem http://www.spoj.com/problems/PLD/ , what is the best way to use rabin_karp?
To precalculate hashes,or add-delete numbers? Cause I am stuck at this 4 hours now... :(
Name |
---|
Substring [l..r] is a palindrome when it equals to its reversed version. So you can precalc hashes for s and for reversed s. Then you may check for all k-substrings if they are equal to its reversed versions.
The time to hash a substring,is the same with pass it with a for loop right? So instead precalculate all hashes,why not to check with naive way??
Except if I calculate the hash via adding and deleting new and last character. I know How to do that in normal string,but in reversing string,I need to delete in reversing mode of rabin-karp.
For example if I have "asd" as string,rabin karp says:
(a*BASE + s)*BASE + d, and when I delete I says -=a*BASE^2.
but in reversing string,I need to delete from the other side,so I should say: -d,and after /=BASE. That gives me strange numbers....
I cant get it!!!
The time to hash a substring,is the same with pass it with a for loop right?
There is a way to calculate polynomial hash of substring in O(1) with O(n) precalc. It's like prefix-sums.
Ok,I figured out !!! Thanks for the time!!!