private static int[][] dir = new int[][]{{-1, 0}, {0, 1}, {1, 0}, {0, -1}};

public int islandPerimeter(int[][] grid) {

if (grid == null || grid.length == 0 || grid[0].length == 0) return 0;

int res = 0;

for (int i=0; i<grid.length; i++) {

for (int j=0; j<grid[0].length; j++) {

if (grid[i][j] == 1) {

res += perimeter(grid, i, j, grid.length, grid[0].length);

}

}

}

return res;

}

private int perimeter(int[][] grid, int i, int j, int n, int m) {

int res = 0;

for (int[] d: dir) {

int x = i + d[0];

int y = j + d[1];

if (x < 0 || x >= n || y < 0 || y >= m || grid[x][y] == 0) {

res++;

}

}

return res;

}

/**

public int islandPerimeter2(int[][] grid) {

int islands = 0, neighbours = 0;

for (int i = 0; i < grid.length; i++) {

for (int j = 0; j < grid[i].length; j++) {

if (grid[i][j] == 1) {

islands++; // count islands

if (i < grid.length - 1 && grid[i + 1][j] == 1) neighbours++; // count down neighbours

if (j < grid[i].length - 1 && grid[i][j + 1] == 1) neighbours++; // count right neighbours

}

}

}

return islands * 4 - neighbours * 2;

}