https://leetcode.com/problems/number-of-islands/#/description
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
Sol:
class Solution(object): def numIslands(self, grid): """ :type grid: List[List[str]] :rtype: int """ # DFS # Iterate through each of the cell and if it is an island, do dfs to mark all adjacent islands, then increase the counter by 1. if not grid: return 0 res = 0 for i in range(len(grid)): for j in range(len(grid[0])): if grid[i][j] == ‘1‘: res += 1 self.dfs(grid, i, j) return res def dfs(self, grid, i, j): if i < 0 or j < 0 or i >= len(grid) or j >= len(grid[0]) or grid[i][j] != ‘1‘: return grid[i][j] = ‘#‘ self.dfs(grid, i+1, j) self.dfs(grid, i-1, j) self.dfs(grid, i, j+1) self.dfs(grid, i, j-1)
Note:
1 Matrix grid is represented by array list, then use grid[i][j] to represent each element.
原文：http://www.cnblogs.com/prmlab/p/7123663.html