題目

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:

難度

Easy

方法

對(duì)于一個(gè)island，如果它有n個(gè)相鄰的island，那它提供的周長(zhǎng)為4-n，將每個(gè)island提供的周長(zhǎng)相加即可

python代碼

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

        return perimeter

assert Solution().islandPerimeter([[0,1,0,0],[1,1,1,0],[0,1,0,0],[1,1,0,0]]) == 16