695. Max Area of Island

static int wing=[]()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();

class Solution 
{
public:
    int maxAreaOfIsland(vector<vector<int>>& grid) 
    {
        int x=grid.size();
        int y=grid[0].size();
        int res=0;
        for(int i=0;i<x;i++)
        {
            for(int j=0;j<y;j++)
            {
                res=max(res,countarea(grid,i,j));
            }
        }
        return res;
    }
    
    int countarea(vector<vector<int>> &grid,int i,int j)
    {
        int szx=grid.size();
        int szy=grid[0].size();
        int count=0;
        if(grid[i][j]==1)
        {
            count++;
            grid[i][j]=0;
            if(valid(i-1,j,szx,szy)) count+=countarea(grid,i-1,j);
            if(valid(i,j-1,szx,szy)) count+=countarea(grid,i,j-1);
            if(valid(i+1,j,szx,szy)) count+=countarea(grid,i+1,j);
            if(valid(i,j+1,szx,szy)) count+=countarea(grid,i,j+1);
            return count;
        }      
        return 0;    
    }
    
    bool valid(int i,int j,int szx,int szy)
    {
        return i>=0&&i<szx&&j>=0&&j<=szy;
    }
    
};

递归，问题不大