```
public class Solution {
public int islandPerimeter(int[][] grid) {
int ans = 0;
for(int i=0; i<grid.length; i++)
for(int j=0; j<grid[0].length; j++)
if(grid[i][j]==1){
if(j-1==-1 || grid[i][j-1]==0) ans++; //left
if(j+1==grid[0].length || grid[i][j+1]==0) ans++; //right
if(i-1==-1 || grid[i-1][j]==0) ans++; //up
if(i+1==grid.length || grid[i+1][j]==0) ans++; //down
}
return ans;
}
```