C++ 代码

class Solution {
public:

    vector<int> printMatrix(vector<vector<int> > matrix) {
        if(matrix.size() == 0 || matrix[0].size() == 0) return vector<int>();

        vector<int> v;
        int n = matrix.size(), m = matrix[0].size();

        int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};
        vector<vector<bool>> flags(n, vector<bool>(m, false));            // 标记已经走过的位置
        int x = 0, y = 0;
        int k = 1;                                                        // 起始方向为 "右"
        for(int i = 0; i < m * n; ++i)
        {
            v.push_back(matrix[x][y]);
            flags[x][y] = true;
            int nx = x + dx[k], ny = y + dy[k];
            if(nx < 0 || nx >= n || ny < 0 || ny >= m || flags[nx][ny])   // 当前位置出界，改变方向
            {
                k = (k + 1) % 4;
                nx = x + dx[k], ny = y + dy[k];                           // 重新计算新坐标的位置
            }

            x = nx;                                                       // 合法坐标
            y = ny;
        }

        return v;
    }
};