[leedcode 200] Number of Islands

public class Solution {
    public int numIslands(char[][] grid) {
        //dfs思想，当发现一个节点是1时，需要将跟其相邻的所有节点置为0，此种方法会改变原grid的值
        if(grid==null||grid.length<=0) return 0;
        int row=grid.length;
        int col=grid[0].length;
        int count=0;
        for(int i=0;i<row;i++){
            for(int j=0;j<col;j++){
                if(grid[i][j]==‘1‘){
                    count++;
                    dfs(grid,i,j);
                }
            }
        }
        return count;
    }
    public void dfs(char[][] grid,int i,int j){
        if(i<0||i>grid.length-1||j<0||j>grid[0].length-1) return;
        if(grid[i][j]==‘1‘){
            grid[i][j]=‘0‘;
            dfs(grid,i-1,j);
            dfs(grid,i+1,j);
            dfs(grid,i,j-1);
            dfs(grid,i,j+1);
        }
    }
}