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;
}
};