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:

11110110101100000000

Answer: 1

Example 2:

11000110000010000011

Answer: 3

大致题意

找出岛屿的数量（1表示陆地）

题解

题目类型：dfs

我们遇到 1 便开始dfs消除关联的陆地，并返回岛屿的大小，如果该岛屿有大小，证明其存在（消除之后算不存在），count + 1

代码如下

class Solution {public:    int numIslands(vector
    
     
      >& grid) {        int count = 0;        for (int i = 0; i < grid.size(); i++) {            for (int j = 0; j < grid[i].size(); j++) {                if (search(i, j, grid)) {                    count ++;                }            }        }        return count;    }    int search(int row, int column, vector
      
       
        >& grid) {        if (row >= 0 && column >= 0 && row < grid.size() && column < grid[row].size() && grid[row][column] == '1') {            grid[row][column] = '0';            return 1 + search(row + 1, column, grid) + search(row - 1, column, grid) + search(row, column + 1, grid) + search(row, column - 1, grid);        }        return 0;    }};