// Source : https://leetcode.com/problems/island-perimeter/

// Author : Han Zichi

// Date : 2016-11-20

/**

* @param {number[][]} grid

* @return {number}

*/

var islandPerimeter = function(grid) {

if (grid.length === 0)

return 0;

let n = grid.length

, m = grid[0].length

, ans = 0;

const dir = [[1, 0], [-1, 0], [0, 1], [0, -1]];

for (let i = 0; i < n; i++)

for (let j = 0; j < m; j++) {

if (!grid[i][j])

continue;

for (let l = 0; l < 4; l++) {

let neighbourCellX = i + dir[l][0];

let neighbourCellY = j + dir[l][1];

if (neighbourCellX < 0 || neighbourCellX >= n

|| neighbourCellY < 0 || neighbourCellY >= m) {

ans += 1;

continue;

}

ans += !grid[neighbourCellX][neighbourCellY];

}

}

return ans;

};