11 - Medium - 岛屿的个数

给定一个由 '1'（陆地）和 '0'（水）组成的的二维网格，计算岛屿的数量。一个岛被水包围，并且它是通过水平方向或垂直方向上相邻的陆地连接而成的。你可以假设网格的四个边均被水包围。

示例 1:

输入:
11110
11010
11000
00000

输出: 1
示例 2:

输入:
11000
11000
00100
00011

输出: 3

循环2维数组，找到其值为1的元素，count++，

然后递归改变其上下左右为1的元素值为0，

class Solution:
    # @param {boolean[][]} grid a boolean 2D matrix
    # @return {int} an integer
    def numIslands(self, grid):
        # Write your code here
        if grid is None: return None
        if grid == []: return 0
        # 当数组不为空时，计算行数和列数
        self.n = len(grid)
        self.m = len(grid[0])
        x = 0
        for i in range(self.n):
            for j in range(self.m):
                if grid[i][j] == '1':
                    x += 1
                    grid = self.change(grid,i,j)
        return x
     
    def change(self,grid,i,j):
        grid[i][j] = '0'
        if i > 0 and grid[i-1][j] == '1':
            # 置当前点上边的点为0
            grid = self.change(grid,i-1,j)
        if i < self.n-1 and grid[i+1][j] == '1':
            # 置当前点下边的点为0
            grid = self.change(grid,i+1,j)
             
        if j < self.m-1 and grid[i][j+1] == '1':
            # 置当前点右方的点为0
            grid = self.change(grid,i,j+1)
        if j > 0 and grid[i][j-1] == '1':
            # 置当前点左方的点为0
            grid = self.change(grid,i,j-1)
        return grid