Number of Islands

Number of Islands
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

这道题的意思给定一个二维数组，里面只包含两个数 0和1，0代表水，1代表陆地，在水平方向和竖直方向相连的1才能代表一块连通的陆地，我们从给出的example中可以看到斜方向上的1不代表相连的陆地。
与其说这是二维数组的题目不如说是图的题目，相当于在一个图中求解包含1的连通子图。我们可以采用深度优先搜索来解决，当我们搜索到1时就把能够和它相连的所有的1都变为‘X’(可以变为任意一个不为1的字符)，这样我们只需要得到遍历中1的个数即可，代码如下：

public class Solution {
    public int numIslands(char[][] grid) {
        if(grid == null || grid.length == 0) return 0;
        int m = grid.length;
        int n = grid[0].length;
        int result = 0;
        for(int i = 0; i < m; i++)
            for(int j = 0; j < n; j++) {
                if(grid[i][j] != '1') continue;
                result ++;
                getResult(grid, i, j);
            }
        return result;
    }
    
    public void getResult(char[][] grid, int i, int j) {
        if(i < 0 || j < 0 || i >= grid.length || j >= grid[0].length) return;
        if(grid[i][j] == '1') {
            grid[i][j] = 'X';
            getResult(grid, i - 1, j);
            getResult(grid, i + 1, j);
            getResult(grid, i, j - 1);
            getResult(grid, i, j + 1);
        }
    }
}