LeetCode #200 - 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

求连通子图的个数，可以从左上角开始遍历，遇见‘1’说明是一个连通子图，然后再将和该点连通的所有‘的1’都变成‘0’，这样遇到的‘1’的个数就是连通子图的个数，同样还是用递归的方法实现对周围点的搜索。

class Solution {
public:
    int numIslands(vector<vector<char> >& grid) 
	{
		int count=0;
		int m=grid.size();
		if(m==0) return 0;
		int n=grid[0].size();
		if(n==0) return 0;
        for(int i=0;i<m;i++)
        {
        	for(int j=0;j<n;j++)
        	{
        		if(grid[i][j]=='1')
        		{
        			searchSurround(grid,i,j);
        			grid[i][j]='0';
        			count++;
        		}
        	}
        }
        return count;
    }
    
    void searchSurround(vector<vector<char> >& grid,int i,int j)
	{
		int m=grid.size();
		int n=grid[0].size();
		if(grid[i][j]!='1') return ;
		if(grid[i][j]=='1') grid[i][j]='0';
		if(i>0) searchSurround(grid,i-1,j);
		if(i+1<m) searchSurround(grid,i+1,j);
		if(j>0) searchSurround(grid,i,j-1);
		if(j+1<n) searchSurround(grid,i,j+1);
	}
};