For each land cell, it contributes 4 to the perimeter. However, if a land cell has a neighbor that is also land, those two share an edge, and we must subtract 2 from the total perimeter (1 for each cell).

1. Initialize perimeter = 0.
2. Iterate through each cell (i, j):
   • If grid[i][j] == 1:
     • perimeter += 4.
     • Check neighbor to the left: if grid[i][j-1] == 1, perimeter -= 2.
     • Check neighbor above: if grid[i-1][j] == 1, perimeter -= 2.
3. Return perimeter.

• Time Complexity: O(M * N).
• Space Complexity: O(1).

def island_perimeter(grid):
    rows, cols = len(grid), len(grid[0])
    perimeter = 0
    
    for r in range(rows):
        for c in range(cols):
            if grid[r][c] == 1:
                perimeter += 4
                # Check top neighbor
                if r > 0 and grid[r - 1][c] == 1:
                    perimeter -= 2
                # Check left neighbor
                if c > 0 and grid[r][c - 1] == 1:
                    perimeter -= 2
                    
    return perimeter