```
class Solution:
# @param {character[][]} grid
# @return {integer}
def numIslands(self, grid):
if not grid:
return 0
m = len(grid)
n = len(grid[0])
nlabel = 2
for i in range(m):
for j in range(n):
# if not labeled
if grid[i][j] == '1':
self.label(nlabel, grid, i, j, m, n)
nlabel += 1
return nlabel - 2
def label(self, nlabel, grid, i, j, m, n):
grid[i][j] = nlabel
# right
if j+1 < n and grid[i][j+1] == '1':
self.label(nlabel, grid, i, j+1, m, n)
# left
if j-1 > -1 and grid[i][j-1] == '1':
self.label(nlabel, grid, i, j-1, m, n)
# down
if i+1 < m and grid[i+1][j] == '1':
self.label(nlabel, grid, i+1, j, m, n)
# up
if i-1 > -1 and grid[i-1][j] == '1':
self.label(nlabel, grid, i-1, j, m, n)
```