ICPC Asia Can Tho Regional Contest 2020 - Open

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2020-12-10 17:00 AKST

## ICPC Asia Can Tho Regional Contest 2020 - Open

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2020-12-10 22:00 AKST
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# Problem HHexagon coloring

You are given a hexagonal grid with $n$ rows, where $n$ is an odd integer. The rows are numbered $1$ to $n$ from top to bottom. The odd-numbered rows have exactly $n$ hexagons, and the even-numbered rows have exactly $n-1$ hexagons. Let’s denote the $j$-th hexagon in the $i$-th row by $(i, j)$.

For example, the below figure shows a hexagonal grid with $n = 3$.

Let’s assign an integer between $-1$ and $6$ to each hexagon. Let’s $a_{i, j}$ be the integer assigned to the hexagon $(i, j)$. The following figure shows one example assignment:

Let’s color some edges of some hexagons. A coloring is valid iff it satisfies the following conditions:

1. For every pair of valid indices $i$ and $j$, either $a_{i, j} = -1$, or $a_{i, j}$ is equal to the number of colored edges of the hexagon $(i, j)$.

2. The colored edges form one or more loops. Each loop must not self-intersect. Two different loops must not share any vertices or edges.

The following figure shows a valid coloring:

The following two figures show two invalid colorings. The one on the left does not satisfy the $1$st condition, and the one on the right does not satisfy the $2$nd condition.

How many valid colorings are there?

## Input

The first line of the input contains a single integer $n$ ($n$ is an odd integer between $1$ and $7$). The next $n$ lines contain the numbers $a_{i, j}$ $(-1 \le a_{i, j} \le 6)$. The $i$-th line contains exactly $n$ integers if $i$ is odd, and $n-1$ integers otherwise.

## Output

Print a single integer — the number of valid colorings.

## Explanation of the sample input

The first sample was shown in the above figures.

The second example is shown below:

Sample Input 1 Sample Output 1
3
-1 2 -1
2 2
1 -1 1

1

Sample Input 2 Sample Output 2
7
-1 4 5 1 0 -1 -1
-1 3 2 0 0 1
-1 4 -1 1 0 -1 -1
1 3 4 2 2 4
0 2 3 -1 4 4 2
-1 4 4 3 3 2
1 -1 -1 -1 4 2 -1

1

Sample Input 3 Sample Output 3
3
-1 2 -1
2 2
-1 -1 -1

4