if (grid.length == 0) return perimeter;

    for (int i = 0; i < grid.length; i++) {
        for (int j = 0; j < grid[i].length; j++) {
            if (grid[i][j] == 1) {
                perimeter += getPerimeter(grid, i - 1, j);
                perimeter += getPerimeter(grid, i + 1, j);
                perimeter += getPerimeter(grid, i, j - 1);
                perimeter += getPerimeter(grid, i, j + 1);
            }
        }
    }
    return perimeter;
}

private int getPerimeter(int[][] grid, int row, int col) {
    if (row < 0 || col < 0 || row >= grid.length || col >= grid[row].length) return 1;

    if (grid[row][col] == 0) return 1;

    return 0;
}