https://www.hackerrank.com/challenges/tutzki-and-lcs/problem
I ve been trying to solve this for hours and could'nt find any understandable online solution, Can anyone explain the logic and code behind this problem.
№ | Пользователь | Рейтинг |
---|---|---|
1 | ecnerwala | 3649 |
2 | Benq | 3581 |
3 | orzdevinwang | 3570 |
4 | Geothermal | 3569 |
4 | cnnfls_csy | 3569 |
6 | tourist | 3565 |
7 | maroonrk | 3531 |
8 | Radewoosh | 3521 |
9 | Um_nik | 3482 |
10 | jiangly | 3468 |
Страны | Города | Организации | Всё → |
№ | Пользователь | Вклад |
---|---|---|
1 | maomao90 | 174 |
2 | awoo | 164 |
3 | adamant | 161 |
4 | TheScrasse | 159 |
5 | nor | 158 |
6 | maroonrk | 156 |
7 | -is-this-fft- | 152 |
8 | SecondThread | 147 |
9 | orz | 146 |
10 | pajenegod | 145 |
https://www.hackerrank.com/challenges/tutzki-and-lcs/problem
I ve been trying to solve this for hours and could'nt find any understandable online solution, Can anyone explain the logic and code behind this problem.
Название |
---|
You just calculate the $$$LCS$$$ as you do.
Let $$$dp1[i][j]$$$ denotes the $$$LCS$$$ of the suffix starting from $$$ith$$$ and $$$jth$$$ index of string $$$a$$$ and $$$b$$$ respectively.
And $$$dp2[i][j]$$$denotes the $$$LCS$$$ of the prefix till $$$ith$$$ and $$$jth$$$ index of string $$$a$$$ and $$$b$$$ respectively.
Now assume we are adding a character before $$$ith$$$ index of string $$$a$$$ to match it with $$$jth$$$ index of string $$$b$$$. Think of the condition for this pair of indexes to contribute to the answer.
$$$dp1[i][j+1] + dp2[i-1][j-1] == LCS$$$
If we implement that condition directly, then it will overcount. Think why is it so?
Only the different number of final $$$a$$$ string formed matters. So, there might be a possibility that you are counting the same character at an index multiple times because that character may appear at different positions in string $$$b$$$.
You can create a $$$vis[i][j]$$$ array to mark $$$1$$$ if you have placed $$$jth$$$ character at index $$$i$$$, and then count the final answer using the number of elements that are marked $$$1$$$ in the $$$vis$$$ array.
Thank you so much brother. I understood your explanation.