# | User | Rating |
---|---|---|
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 |
# | User | Contrib. |
---|---|---|
1 | maomao90 | 173 |
2 | adamant | 164 |
3 | awoo | 161 |
4 | TheScrasse | 160 |
5 | nor | 159 |
6 | maroonrk | 156 |
7 | SecondThread | 152 |
8 | pajenegod | 146 |
9 | BledDest | 144 |
10 | Um_nik | 143 |
This question was featured in a ICPC Regional Contest. To summarize briefly, it gives a string consisting of 3 possible letters, 'I' (which stands for increasing), 'D' (decreasing) and/or '?' (both 'I' or 'D') to represent two consecutive numbers of an n-permutation (1 to n). Ex. the string 'IID' can fit the 4-permutations {1,3,4,2}, {1,2,4,3} and {2,3,4,1}. The task is given a string, find the number of possible permutations that fit the string in mod 10^9 + 7.
A working solution is found here. Can someone please clarify the recurrence relation to solve this dp?
Name |
---|