LC463. Island Perimeter

Approach: Iterating and checking for shores

class Solution:
    def islandPerimeter(self, grid: List[List[int]]) -> int:
        m, n = len(grid), len(grid[0])
 
        def not_land(i, j):
            if 0 <= i < m and 0 <= j < n:
                return grid[i][j] == 0
            
            return 1
 
        perim = 0
 
        for i in range(m):
            for j in range(n):
                if grid[i][j] == 1:
                    perim += int(not_land(i - 1, j)) + \
                            int(not_land(i + 1, j)) + \
                            int(not_land(i, j + 1)) + \
                            int(not_land(i, j - 1))
        
        return perim

Complexity

Time: $O(n)$ - where $n$ is the number of cells in the grid.
Space: $O(1)$