题目要求

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.

题目分析及思路

题目给出二维整数数组，1代表土地，0代表水域。要求土地互相连接只能形成一个岛屿，然后被水域包围，内部不能含有水域。最后返回这个岛屿的周长。要计算岛屿的周长，其实可以将每个土地的周长求和，再减去邻接的个数的两倍。

python代码

class Solution:

    def islandPerimeter(self, grid: List[List[int]]) -> int:

        lands, neighbors = 0, 0

        rows = len(grid)

        cols = len(grid[0])

        for r in range(rows):

            for c in range(cols):

                if grid[r][c] == 1:

                    lands += 1

                    if r < rows - 1:

                        if grid[r+1][c] == 1:

                            neighbors += 1

                    if c < cols - 1:

                        if grid[r][c+1] == 1:

                            neighbors += 1

        return 4 * lands - 2 * neighbors