LeetCode:Number of Islands

题目描述：

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

思路分析：依次用DFS找到属于同一岛屿的所有元素，并将它们标记起来。

代码：

class Solution
{
	public:

		void dfs(vector<vector<char> > & grid,int x,int y)
		{
			if(x < 0 || x >= grid.size() || y < 0 || y >= grid[0].size())
				return;
			if(grid[x][y] == '1')
			{
				grid[x][y] = 'x';
				dfs(grid,x+1,y);
				dfs(grid,x-1,y);
				dfs(grid,x,y+1);
				dfs(grid,x,y-1);
			}
		}

		int numIslands(vector<vector<char> > & grid)
		{
			int islands_number = 0;
			for(int i = 0;i < grid.size();i++)
				for(int j = 0;j < grid[0].size();j++)
				{
					if(grid[i][j] == '1')
					{
						dfs(grid,i,j);
						islands_number++;
					}
				}
			return islands_number;
		}
};

LeetCode:Number of Islands

原文：http://blog.csdn.net/yao_wust/article/details/45670959