C++ 代码 姑且称之为遍历即可

class Solution {
public:
    vector<int> printMatrix(vector<vector<int> > matrix) {
        vector<int> res;
        if(matrix.size() == 0 || matrix[0].size() == 0) return res;
        int n = matrix.size();  // 行
        int m = matrix[0].size(); //列

        vector<vector<bool>> b(n,vector<bool>(m,false));

        int d[4][2] = {
            {0,1}, //right
            {1,0}, // down
            {0,-1}, //left
            {-1,0} //up
        };

        int x = 0 , y = 0;
        int k = 0; //k:0-3

        res.push_back(matrix[0][0]);
        b[0][0] = true;

        for(int i = 0; i < m*n - 1; i++){
            x += d[k][0];
            y += d[k][1];

            if(x >= 0 && x < n && y >= 0 && y < m && (!b[x][y])){
                res.push_back(matrix[x][y]);
                b[x][y] = true;
            }
            else{//回退
                x -= d[k][0];
                y -= d[k][1];    
                k = (k + 1) % 4;
                i--;
            }
        }

        return res;
    }
};