Find node neighbors in 2d array

Question

Assume that I have the following (n * n) array:

1 2 3 4
5 6 7 8
9 a b c
d e f g

I want to write a function that finds the neighbor nodes of a given node. For example, for node 1, it will return an array with 2, 6, and 5. For node "a", it will return a vector with node 5, 6, 7, b, f, e, d, and 9. The order does not matter. I tried to do this with only using if-statements, but it turned into a nightmare really quick.

Whats the best way to approach this problem?

Answer 1

// assume (x,y) is position in array you want to get neighbours from
// assume 'array' is your array with x first and then y
// assume T is type of your array stuff

ArrayList<T> list = new ArrayList<T>();

for (int i = x - 1; i <= x + 1; i++) {
    for (int j = y - 1; j <= y + 1; j++) {
        // check if (i,j) is in array bounds
        if (i >= 0 && j >= 0 && i < array.length() && j < array[i].length()) {
            // the point isn't its own neighbour
            if (i != x && j != y)
                list.add(array[i][j]);
        }
    }
}
return list.toArray();

EDIT: As your Array is n*n big you don't have to use array.length(), but this way it will work for all kind of array.

Answer 2

you can use for loops, let assume that (i,j) is the location of your element, mat is your array

mat[n][n]
int res[8];
int x = 0;
for (int k = i - 1 ; k < 2 ;k++)
    for(int t = j-1 ; j  <2 ;j++)
        if ((k > 0) && (t > 0) && (t<n) && (k < n))
            res[x++] = mat[k][t];