顺时针打印矩阵

class Printer {
public:
    vector<int> clockwisePrint(vector<vector<int> > mat, int n, int m) {
        // write code here
        vector<int> v;
        printHelper(mat, n, m, 0, 0, v);
        return v;
    }
    
    void printHelper(vector<vector<int>> mat, int n, int m, int x, int y, vector<int> &v) {
        
　　　　　if(x == n || y == m) return;
        for(int j = y; j < m; ++j) {
            v.push_back(mat[x][j]);
        }
        for(int i = x + 1; i < n; ++i) {
            v.push_back(mat[i][m - 1]);
        }
        for(int j = m - 2; j >= y; --j) {
            v.push_back(mat[n - 1][j]);
        }
        for(int i = n - 2; i >= x + 1; --i) {
            v.push_back(mat[i][y]);
        }
        printHelper(mat, n - 1, m - 1, x + 1, y + 1, v);
    }
};