Problem7290--AtCoder Educational DP Contest —— R - Walk

7290: AtCoder Educational DP Contest —— R - Walk

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Time Limit : 1.000 sec  Memory Limit : 256 MiB

Description

There is a simple directed graph G with $N$ vertices, numbered $1,2,…,N$.
For each $i$ and $j\ (1≤i,j≤N)$, you are given an integer $a_{i, j}$ that represents whether there is a directed edge from Vertex $i$ to $j$. If $a_{i, j} = 1$, there is a directed edge from Vertex $i$ to $j$; if $a_{i, j} = 0$, there is not.
Find the number of different directed paths of length $K$ in G, modulo $10^9 + 7$. We will also count a path that traverses the same edge multiple times.

Input

Input is given from Standard Input in the following format:
$N\ K$
$a_{1, 1}\ \ldots\ a_{1, N}$
$:$
$a_{N, 1}\ \ldots\ a_{N, N}$

Output

Print the number of different directed paths of length $K$ in G, modulo $10^9 + 7$.

Constraints

All values in input are integers.
$1 \leq N \leq 50$
$1 \leq K \leq 10^{18}$
$a_{i, j}$ is 0 or 1.
$a_{i, i}$ = 0

Sample 1 Input

4 2
0 1 0 0
0 0 1 1
0 0 0 1
1 0 0 0

Sample 1 Output

6
G is drawn in the figure below:

There are six directed paths of length 2:
  • 1 → 2 → 3
  • 1 → 2 → 4
  • 2 → 3 → 4
  • 2 → 4 → 1
  • 3 → 4 → 1
  • 4 → 1 → 2

Sample 2 Input

3 3
0 1 0
1 0 1
0 0 0

Sample 2 Output

3
G is drawn in the figure below:

There are three directed paths of length 3:
  • 1 → 2 → 1 → 2
  • 2 → 1 → 2 → 1
  • 2 → 1 → 2 → 3

Sample 3 Input

6 2
0 0 0 0 0 0
0 0 1 0 0 0
0 0 0 0 0 0
0 0 0 0 1 0
0 0 0 0 0 1
0 0 0 0 0 0

Sample 3 Output

1
G is drawn in the figure below:

There is one directed path of length 2:
  • 4 → 5 → 6

1 1
0

0

Sample 4 Input

10 1000000000000000000
0 0 1 1 0 0 0 1 1 0
0 0 0 0 0 1 1 1 0 0
0 1 0 0 0 1 0 1 0 1
1 1 1 0 1 1 0 1 1 0
0 1 1 1 0 1 0 1 1 1
0 0 0 1 0 0 1 0 1 0
0 0 0 1 1 0 0 1 0 1
1 0 0 0 1 0 1 0 0 0
0 0 0 0 0 1 0 0 0 0
1 0 1 1 1 0 1 1 1 0

Sample 4 Output

957538352

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