NumberOfIslandsI origianl questions：求岛屿数量 leetcode原题

public class NumberOfIslandsI {
private int m,n;

public int numIslands(char[][] grid) {
m=grid.length;
if(m==0)return 0;
n=grid[0].length;
if(n==0)return 0;
int ans=0;
for(int i=0;i<m;i++){
for(int j=0;j<n;j++){
if(grid[i][j]!='1')continue;
ans++;
DFS(grid,i,j);
}
}
return ans;
}


public void DFS(char[][]grid,int i,int j){
if(i<0||i>=m||j<0||j>=n)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);
}
}

}