Number fo Islands

    static Integer count_islands(ArrayList<ArrayList<Integer>> matrix) {
        int nr = matrix.size();
        int nc = matrix.get(0).size();

        boolean[][] visited = new boolean[nr][nc];

        int number_of_islands = 0;
        for (int i = 0; i < nr; i++) {
            for (int j = 0; j < nc; j++) {
                if (!visited[i][j] && matrix.get(i).get(j) == 1) {
                    bfs(i, j, matrix, visited);
                    number_of_islands += 1;
                }
            }
        }

        return number_of_islands;
    }

    static void bfs(int i, int j, ArrayList<ArrayList<Integer>> matrix, boolean[][] visited) {
        visited[i][j] = true;
        Queue<int[]> q = new LinkedList<int[]>();
        q.offer(new int[]{i,j});
        while (!q.isEmpty()) {
            int[] curr = q.poll();
            int curr_i = curr[0];
            int curr_j = curr[1];
            for (int[] neighbor : getNeighbors(curr_i, curr_j, matrix)) {
                int n_i = neighbor[0];
                int n_j = neighbor[1];
                if (!visited[n_i][n_j]) {
                    q.offer(new int[]{n_i, n_j});
                    visited[n_i][n_j] = true;
                }
            }
        }
    }

    static ArrayList<int[]> getNeighbors(int i, int j, ArrayList<ArrayList<Integer>> matrix) {
        int nr = matrix.size();
        int nc = matrix.get(0).size();

        ArrayList<int[]> neighbors = new ArrayList<int[]>();

        if (i - 1 >= 0 && i - 1 <= nr - 1 && matrix.get(i - 1).get(j) == 1) {
            neighbors.add(new int[]{i - 1, j});
        }

        if (i + 1 >= 0 && i + 1 <= nr - 1 && matrix.get(i + 1).get(j) == 1) {
            neighbors.add(new int[]{i + 1, j});
        }

        if (j - 1 >= 0 && j - 1 <= nc - 1 && matrix.get(i).get(j - 1) == 1) {
            neighbors.add(new int[]{i, j - 1});
        }

        if (j + 1 >= 0 && j + 1 <= nc - 1 && matrix.get(i).get(j + 1) == 1) {
            neighbors.add(new int[]{i, j + 1});
        }

        return neighbors;
    }