解题代码：

class Solution {
public:vector<int> spiralOrder(vector<vector<int>>& matrix) {if (matrix.empty() || matrix[0].empty()) return {};int m = matrix.size(), n = matrix[0].size();vector<int> res;int up = 0, down = m - 1, left = 0, right = n - 1;while (true) {for (int j = left; j <= right; ++j) res.push_back(matrix[up][j]);if (++up > down) break;for (int i = up; i <= down; ++i) res.push_back(matrix[i][right]);if (--right < left) break;for (int j = right; j >= left; --j) res.push_back(matrix[down][j]);if (--down < up) break;for (int i = down; i >= up; --i) res.push_back(matrix[i][left]);if (++left > right) break;}return res;}
};