顺时针打印矩阵

输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字。

class Solution {
public:
    int dx[4] = {0, 1, 0, -1};
    int dy[4] = {1, 0, -1, 0};
    int x1, x2, y1, y2;
    
    bool in (int x, int y) {
        return x1 <= x && x < x2 && y1 <= y && y < y2;
    }
    
    void change (int k) {
        if (k == 0) x1++;
        else if (k == 1) y2--;
        else if (k == 2) x2--;
        else y1++;
    }
    
    vector<int> printMatrix(vector<vector<int> > g) {
        if (!g.size() || !g[0].size()) return {};
        x2 = g.size(), y2 = g[0].size();
        int len = x2 * y2;
        
        vector<int> ans;
        int x = 0, y = -1, k = 0;
        for (int i = 0; i < len; i++) {
            x += dx[k], y += dy[k];
            
            if (in(x, y)) {
                ans.push_back(g[x][y]);
            }
            else {
                x -= dx[k], y -= dy[k];
                change(k);
                k = (k + 1) % 4;
                x += dx[k], y += dy[k];
                ans.push_back(g[x][y]);
            }
            
        }
        
        return ans;
    }
};