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 horizontally/vertically (not diagonally). 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:

分析：计算给出图形的周长，不存在孤岛。

思路：统计相邻岛屿数分别为0，1，2，3的个数。计算公式：s0*4+s1*3+s2*2+s4*1

JAVA CODE：

class Solution {
    public int islandPerimeter(int[][] grid) {
        int s0 = 0, s1 = 0, s2 = 0, s3 = 0;
        for(int i = 0; i < grid.length; i++){
            for(int j = 0; j < grid[0].length; j++){
                int m = grid[i][j];
                if(m == 0)
                    continue;
                int s = 0;
                if(i > 0 && grid[i - 1][j] == 1)
                    s++;
                if(i < grid.length - 1 && grid[i + 1][j] == 1)
                    s++;
                if(j > 0 && grid[i][j - 1] == 1)
                    s++;
                if(j < grid[0].length - 1 && grid[i][j + 1] == 1)
                    s++;
                if(s == 0)
                    s0++;
                if(s == 1)
                    s1++;
                if(s == 2)
                    s2++;
                if(s == 3)
                    s3++;
            }
        }
        return s0 * 4 + s1 * 3 + s2 * 2 + s3 * 1;
    }
}