Hiring process8 levels
  1. 1 IQ Test
  2. 2 Additional Online Test (If Required)
  3. 3 Office Interview with Hiring Manager
  4. 4 Unpaid Test Task (Motivation Check)
  5. 5 Paid Test Task and Follow-Up Interview
  6. 6 Iterative Paid Test Tasks
  7. 7 Office Verification
  8. 8 Final Interview with the Founder

Problems > Binary Strings Avoiding 111

Binary Strings Avoiding 111

Difficulty: 1600 4000 ms 128 MB

combinatorics matrix-exponentiation

Count the binary strings of length N with no three consecutive 1s, modulo 109+7.

Input: one integer N.

Output: the count modulo 109+7.

Constraints:

  • 1 ≤ N ≤ 1018

Sample Tests

Input 1
1
Output 1
2
Input 2
2
Output 2
4
Input 3
3
Output 3
7
Input 4
4
Output 4
13

Read the Editorial Statistics

Discussion (opens after you solve — no spoilers before)

No comments yet.

Submit Your Solution

Log in or create a free account to run and submit code.
Ctrl+Enter submit · Ctrl+Space autocomplete · F11 fullscreen