463. 岛屿的周长

思路

一个陆地的周长为4

如果这个陆地上、下、左、右有陆地相连，则这个岛屿的周长=4-相邻陆地的边的长度

class Solution(object):
    def islandPerimeter(self, grid):
        """
        :type grid: List[List[int]]
        :rtype: int
        """
        row=len(grid)
        col=len(grid[0])
        area=0
        for i in range(row):
            for j in range(col):
                if grid[i][j]==1:
                    t=4
                    if i-1>=0 and grid[i-1][j]==1:
                        t-=1
                    if i+1<row and grid[i+1][j]==1:
                        t-=1
                    if j-1>=0 and grid[i][j-1]==1:
                        t-=1
                    if j+1<col and grid[i][j+1]==1:
                        t-=1
                    area+=t
        return area