IslandPerimeter.java

public class IslandPerimeter {
    public static void main(String[] args) { // for tests
        int p = new IslandPerimeter().islandPerimeter(new int[][]{{0,1,0,0},{1,1,1,0},{0,1,0,0},{1,1,0,0}});

        System.out.println(p);
    }
    
    public int islandPerimeter(int[][] grid) {
        int perimeter = 0;
        for(int i = 0; i < grid.length; i++) {
            int[] row = grid[i];
            for(int j = 0; j < row.length; j++) {
                if(row[j] == 0) continue;
                int toAdd = 4;
                if(i != 0 && grid[i-1][j] == 1) toAdd -= 1;
                if(i+1 != grid.length && grid[i+1][j] == 1) toAdd -= 1;
                if(j != 0 && grid[i][j-1] == 1) toAdd -= 1;
                if(j+1 != row.length && grid[i][j+1] == 1) toAdd -= 1;
                perimeter += toAdd;
            }
        }
        return perimeter;
    }
}