When I submit my program I get an error but when I use the same input that is used for testing in custom test case my program works fine. Is there a buy in the testing machine ?This is my version of the code:

```
visited = set([])
class Solution(object):
def numIslands(self, grid):
"""
:type grid: List[List[str]]
:rtype: int
"""
if len( grid ) == 0:
return 0
global count
m = len( grid )
n = len( grid[0] )
#print m
#print n
rvec = [-1,0,1,0]
cvec = [ 0,1,0,-1]
count = 0
for i in range(m):
for j in range(n):
if grid[i][j] == '0':
continue
count += self.recurse( grid, m , n , rvec, cvec, i , j )
return count
def recurse( self, grid, m , n,rvec, cvec, i, j):
global visited
if str(i) + str(j) in visited:
return 0
visited.add( str(i) + str(j) )
for r,c in map( None, rvec, cvec ):
nx = r + i
ny = c + j
if nx >= 0 and nx < m and ny >= 0 and ny < n and ( str(nx) + str(ny) ) not in visited and grid[nx][ny] != '0':
self.recurse( grid, m ,n ,rvec, cvec, nx, ny )
return 1
```