void infect(vector<vector<int>>& arr,int i,int j)
{
    /******注意边界******/
    if(i > arr.size() || i < 0 || j > arr[0].size() || j < 0 || arr[i][j] != 1) return;
    arr[i][j] = 2;
    infect(arr,i - 1,j);
    infect(arr,i + 1,j);
    infect(arr,i,j + 1);
    infect(arr,i,j - 1);
}
​
int Island(vector<vector<int>> arr)
{
    int res = 0;
    for(int i = 0;i < arr.size();i++)
    {
        for(int j = 0;j < arr[0].size();j++)
        {
            if(arr[i][j] == 1)
            {
                res++;
                infect(arr,i,j);
            }
        }
    }
    return res;
}