Code Word
Time limit1sMemory limit512 MB
Count length-l digit sequences on an r by c grid where no two consecutive presses are orthogonally or diagonally adjacent, mod 1e9+7.
- Level
Medium5 of 10
- Topics
- Dynamic programming, Matrix, Combinatorics, Implementation
- Solved
- No attempts yet
Problem
Following on from the engineering success of Left Pad, Ltd, Lynn started a new venture: Internet of Security, Inc. The company's flagship product will be a device for entering passcodes.
The chief innovation of this device will be in its ability to reject attempts to set insecure passwords. An insecure passcode is defined as a sequence of digit presses such that at least two consecutive presses are either directly or diagonally adjacent.
Lynn, ever-vigilant for the future, is worried that this system might not allow enough unique passcodes to support a large company with trillions of employees. For a given digit pad grid size, and fixed length of password, calculate the number of allowed passwords.
Since the number might be very large in some cases, output your answer mod 1 000 000 007.
Input
- The first line contains the integers r and c (1 ≤ r, c ≤ 100), the number of rows and columns of buttons on the pad.
- The second line contains the integer l (1 ≤ l ≤ 200), the single allowed length for any passcode.
Output
Output the number of legal passcodes, mod 1 000 000 007.