Time Complexity - O(m*n)

Space Complexity - O(1)

- m = num of rows
- n = num of cols

```
def island_perimeter(grid)
land, neighbors = 0, 0
num_rows = grid.length
num_cols = grid.first.length
(0...num_rows).each do |row_idx|
(0...num_cols).each do |col_idx|
if grid[row_idx][col_idx] == 1
land += 1
if row_idx + 1 < num_rows && grid[row_idx + 1][col_idx] == 1
neighbors += 1
end
if col_idx + 1 < num_cols && grid[row_idx][col_idx + 1] == 1
neighbors += 1
end
end
end
end
(land * 4) - (neighbors * 2)
end
```