c++ DFS

class Solution {
public:
        int a[50][50];
        int n=0;
        bool in(int x,int y,int k)
        {
            if(x/10+x%10+y/10+y%10>k)
                return false;
            else
                return true;
        }
        void dfs(int x,int y,int rows,int cols,int k)
        {
            if(x<0||x>rows-1||y<0||y>cols-1||!in(x,y,k)||a[x][y]==1)
                return;
                n++;
                a[x][y]=1;
                dfs(x-1,y,rows,cols,k);dfs(x,y-1,rows,cols,k);
                dfs(x+1,y,rows,cols,k);dfs(x,y+1,rows,cols,k);  

        }
        int movingCount(int threshold, int rows, int cols)
        {
            dfs(0,0,rows,cols,threshold);
            return n;
        }
};