Leetcode 200. number of Islands

 1 class Solution(object):
 2 
 3     def numIslands(self, grid):
 4         """
 5         :type grid: List[List[str]]
 6         :rtype: int
 7         """
 8         m = len(grid)
 9         if m == 0:
10             return 0
11         n = len(grid[0])
12         
13         ans = 0
14         for i in range(m):
15             for j in range(n):
16                 if grid[i][j] == ‘1‘:
17                     ans += 1
18                     self.helper(grid, m, n, i, j)
19                 
20         return ans
21         
22     def helper(self, grid, m, n, i, j):
23         if (i < 0 or j < 0 or i > m-1 or j > n-1):
24             return 
25         
26         if grid[i][j] == ‘1‘:
27             grid[i][j] = ‘2‘
28             self.helper(grid, m, n, i-1, j)
29             self.helper(grid, m, n, i+1, j )
30             self.helper(grid, m, n, i, j-1)
31             self.helper(grid, m, n, i, j+1)

 1 class Solution(object):
 2     def numIslands(self, grid):
 3         """
 4         :type grid: List[List[str]]
 5         :rtype: int
 6         """
 7         m = len(grid)
 8         if m == 0:
 9             return 0
10         n = len(grid[0])
11         visited = [ [False]* n for x in range(m)]
12         ans = 0
13         for i in range(m):
14             for j in range(n):
15                 if grid[i][j] == ‘1‘ and visited[i][j] == False:
16                     ans += 1
17                     self.bfs(grid, visited, m, n, i, j)
18                 
19         return ans
20         
21     def bfs(self, grid, visited, m, n, i, j):
22         direct = [[0,1],[0,-1],[1,0],[-1,0]]
23         queue = [[i, j]]
24         visited[i][j] = True
25         
26         while queue:
27             front = queue.pop(0)
28             for p in direct:
29                 np = [front[0]+p[0], front[1]+p[1]]
30                 if self.isValid(np, m, n) and grid[np[0]][np[1]] == ‘1‘31                 and visited[np[0]][np[1]] == False:
32                     visited[np[0]][np[1]] = True
33                     queue.append(np)
34     
35     def isValid(self, np, m, n):
36         return np[0]>=0 and np[0]<m and np[1]>=0 and np[1]<n