200. Number of Islands Leetcode Python

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

Example 1:

11110
11010
11000
00000

Answer: 1

Example 2:

11000
11000
00100
00011

Answer: 3

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

We can do DFS in this problem and mark the position as visited everytime.  out of the DFS count the island.

class Solution:
    # @param grid, a list of list of characters
    # @return an integer
    def numIslands(self, grid):
        m = len(grid)
        if m == 0:
            return 0
        n = len(grid[0])
        visit = [[False for i in range(n)]for j in range(m)]
        def check(x, y):
            if x >= 0 and x<m and y>= 0 and y< n and grid[x][y] == '1' and visit[x][y] == False:
                return True
        def dfs(x,y):
            nbrow = [1,0,-1,0]
            nbcol = [0,1,0,-1]
            for k in range(4):
                newx = x + nbrow[k]
                newy = y + nbcol[k]
                if check(newx, newy):
                    visit[newx][newy] = True
                    dfs(newx,newy)
        count = 0
        for row in range(m):
            for col in range(n):
                if check(row,col):
                    visit[row][col] = True
                    dfs(row,col)
                    count+=1
        return count