[LeetCode]463. Island Perimeter

题目

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:

难度

Easy

方法

对于一个island，如果它有n个相邻的island，那它提供的周长为4-n，将每个island提供的周长相加即可

python代码

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