463. Island Perimeter

题目大意：求岛屿的周长，给定一个二维数组，“1”代表土地，“0”代表水，“土地”与“土地”之间一定是相连的，“土地”也不会包围着“水”，每一块土地的边长为1，在一个正方形的区域中，长和宽都不会超过100，示例见下图

463. Island Perimeter

You are given a map in form of a two-dimensional integer grid where 1 represents land and 0 represents water. Grid cells are connected The grid is completely surrounded by water, and there is exactly one island (i.e., one or more connected land cells). The island doesn't have "lakes" (water inside that isn't connected to the water around the island). One cell is a square with side length 1. The grid is rectangular, width and height don't exceed 100. Determine the perimeter of the island.

Example:

[ [ 0 , 1 , 0 , 0 ] ,

[ 1 , 1 , 1 , 0 ] ,

[ 0 , 1 , 0 , 0 ] ,

[ 1 , 1 , 0 , 0 ] ]

Answer: 16

Explanation: The perimeter is the 16 yellow stripes in the image below:

public int islandPerimeter(int[][] grid) {
    int per = 0;
    for (int i = 0; i < grid.length; i ++) {
        for (int j = 0; j < grid[0].length; j ++) {
            if (grid[i][j] == 1) {
                // top
                if (j == 0 || grid[i][j - 1] == 0) per ++;
                // left
                if (i == 0 || grid[i - 1][j] == 0) per ++;
                // bottom
                if (j == grid[0].length - 1 || grid[i][j + 1] == 0) per ++;
                // right
                if (i == grid.length - 1 || grid[i + 1][j] == 0) per ++;
            }
        }
    }
    return per;
}