leetcode-Number of Islands

Number of Islands

题目详情：

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

解题方法：

从给的例子可以看出，就是寻找共有多少块不相邻的“1”的组。从二维数组中第一个member开始遍历每一个member，如果这member是陆地且没有被访问过，则对它进行dfs，递归的dfs它的四个邻居。这样的dfs的个数就是不相邻的“1”的组的个数。

代码详情：

class Solution {
public:
    int numIslands(vector<vector<char>>& grid) {
        int n = grid.size();
        if (n == 0) return 0;
        int m = grid[0].size();
        if (m == 0) return 0;
        vector<vector<bool> > visited(n, vector<bool>(m, false));
        int res = 0;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (grid[i][j] == '1' && !visited[i][j]) {
                    dfs(grid, visited, i, j);
                    res++;
                }
            }
        }
        return res;
    }
    void dfs(vector<vector<char>>& grid, vector<vector<bool> >& visited, int x, int y) {
        if (x < 0 || x >= grid.size()) return;
        if (y < 0 || y >= grid[0].size()) return;
        if (grid[x][y] != '1' || visited[x][y]) return;
        visited[x][y] = true;
        dfs(grid, visited, x-1, y);
        dfs(grid, visited, x+1, y);
        dfs(grid, visited, x, y-1);
        dfs(grid, visited, x, y+1);
    }
    
};