leetcode算法：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:

题目的意思是，给定某个二维数组，里面全是1和0
1 代表陆地 0代表海洋。相邻的1就是连着的陆地。
把每块陆地想成正方形，边长是1。
现在给定某个二维数组grid，我们来算出相连陆地的总周长。

思想就是遍历整个二位数组，对于每一个数，如果他是陆地 就看他的四周，有一个方向不是陆地 周长就加1

我的代码：

 class Solution(object):
     def islandPerimeter(self, grid):
         """
         :type grid: List[List[int]]
         :rtype: int
         """
         res = 0
         for i in range(len(grid)):
             for j in range(len(grid[0])):
                 if grid[i][j] == 1:
                     if i == 0 or grid[i-1][j] == 0:
                         res +=1
                     if i==len(grid)-1 or grid[i+1][j]==0:
                         res +=1
                     if j==0 or grid[i][j-1] ==0:
                         res +=1
                     if j==len(grid[0])-1 or grid[i][j+1]==0:
                         res += 1
         return res

 if __name__ == '__main__':
     s = Solution()
     res = s.islandPerimeter( [
                      [0,1,0,0],
                      [1,1,1,0],
                      [0,1,0,0],
                      [1,1,0,0]
                 ])
     print(res)