[Python手撕]岛屿数量

给你一个由 '1'（陆地）和 '0'（水）组成的的二维网格，请你计算网格中岛屿的数量。
岛屿总是被水包围，并且每座岛屿只能由水平方向和/或竖直方向上相邻的陆地连接形成。
此外，你可以假设该网格的四条边均被水包围。

示例 1：

输入：grid = [
["1","1","1","1","0"],
["1","1","0","1","0"],
["1","1","0","0","0"],
["0","0","0","0","0"]
]
输出：1
示例 2：

输入：grid = [
["1","1","0","0","0"],
["1","1","0","0","0"],
["0","0","1","0","0"],
["0","0","0","1","1"]
]
输出：3

class Solution:
    def numIslands(self, grid: List[List[str]]) -> int:

        n = len(grid)
        m = len(grid[0])


        def eliminate(x,y):
            if 0<=x<n and 0<=y<m and grid[x][y] == "1":
                grid[x][y] = "0"

                eliminate(x+1,y)
                eliminate(x, y+1)
                eliminate(x - 1, y)
                eliminate(x, y-1)

        count = 0
        for i in range(n):
            for j in range(m):
                if grid[i][j] == "1":
                    eliminate(i,j)
                    count += 1
        
        return count