200. Number of Islands

题目地址：https://leetcode.com/problems/number-of-islands/description/
大意：观察一个二维矩阵里面'1'的块数

例
用DFS的方法，遍历。

# 200. Number of Islands

class Solution:
    def numIslands(self, grid):
        """
        :type grid: List[List[str]]
        :rtype: int
        """
        m = len(grid)
        if m == 0:
            return 0
        n = len(grid[0])
        ans = 0
        for y in range(m):
            for x in range(n):
                if grid[y][x] == '1':
                    ans += 1
                    self.__dfs(grid, x, y, n, m)
        return ans


    def __dfs(self,grid,x,y,n,m):
        if x<0 or y<0 or x >= n or y>=m or grid[y][x] == '0':
            return
        grid[y][x] = '0'
        self.__dfs(grid, x + 1, y, n, m)
        self.__dfs(grid, x - 1, y, n, m)
        self.__dfs(grid, x, y + 1, n, m)
        self.__dfs(grid, x, y - 1, n, m)

a = Solution()
print (a.numIslands([['1','1','0','0','0'],['1','1','0','0','0'],['0','0','1','0','0'],['0','0','0','1','1']]))