参考了答案。。。。。。

思路：深度优先遍历，对每个是陆地且未曾访问过的位置进行dfs，每进行一次，岛屿数量加一

code:

class Solution {private static final int[][] dir = {{-1, 0}, {0, -1}, {1, 0}, {0, 1}};private boolean[][] visited;private int rows;private int cols;private char[][] grid;public int numIslands(char[][] grid) {rows=grid.length;if(rows==0){return 0;}cols=grid[0].length;this.grid=grid;visited=new boolean[rows][cols];int count=0;for(int i=0;i<rows;i++){for(int j=0;j<cols;j++){if(!visited[i][j]&&grid[i][j]=='1'){dfs(i,j);count++;}}}return count;}public void dfs(int i,int j){visited[i][j]=true;for(int k=0;k<4;k++){int newx=i+dir[k][0];int newy=j+dir[k][1];if(0<=newx&&newx<rows&&0<=newy&&newy<cols&&!visited[newx][newy]&&grid[newx][newy]=='1'){dfs(newx,newy);}}}
}