Binary Strings Avoiding 1000
combinatorics kmp matrix-exponentiation
Count the binary strings of length N with no contiguous occurrence of 1000, modulo 109+7.
Input: one integer N.
Output: the count mod 109+7.
Constraints:
- 1 ≤ N ≤ 1018
Sample Tests
Input 1
2
Output 1
4
Input 2
3
Output 2
8
Input 3
5
Output 3
28
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