顺时针打印矩阵

class Solution {
public:
    int turn,n,m;
    static const int N=410;
    int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0};//右下左上
    bool st[N][N];
    bool check(int i,int j)
    {
        if(i<0||i>=n||j<0||j>=m)    return false;
        if(st[i][j]==true)  return false;
        return true;
    }
    vector<int> printMatrix(vector<vector<int> > g) {
        vector<int> q;
        if(g.size()==0||g[0].size()==0) return q;
        n=g.size(),m=g[0].size();
        int len=n*m,i=0,j=0;
        while(len--)
        {
            st[i][j]=true;
            q.push_back(g[i][j]);
            int x=i+dx[turn],y=j+dy[turn];
            if(!check(x,y))
            {
                turn=(turn+1)%4;
                x=i+dx[turn],y=j+dy[turn];
            }
            i=x;j=y;
        }
        return q;
    }
};