class Solution {public:    vector<int> spiralOrder(vector<vector<int> > &matrix) {        vector<int> result;        int nRows = matrix.size();        if (nRows == 0) return result;        int nCols = matrix.at(0).size();        result.reserve(nRows * nCols);                int startX = 0;        int startY = 0;                while (nRows > 2 * startX  && nCols > 2 * startY) {            PrintNumbers(matrix, startX, startY, result);            ++startX;            ++startY;        }        return result;            }        void PrintNumbers(vector<vector<int>>& matrix, int startX, int startY, vector<int>& result) {            assert(startX >= 0 && startY >= 0);            int nRows = matrix.size();            int nCols = matrix.at(0).size();                        int rowLen = nRows - 2 * startX; // 当前矩形的长度            int colLen = nCols - 2 * startY; // 当前矩形的宽度                        int endX = startX + colLen - 1;  // endX - startX + 1 = colLen X为横坐标            int endY = startY + rowLen - 1;  // endY - startY + 1 = rowLen Y为纵坐标                        // 1. 从左往右            for (int i = startX; i <= endX; ++i) {                result.push_back(matrix.at(startY).at(i));            }                        // 2. 从上往下            if (endY > startY) {                for (int i = startY + 1; i <= endY; ++i) {                    result.push_back(matrix.at(i).at(endX));                }            }                        // 3. 从右往左            if (endX > startX && endY > startY) {                for (int i = endX - 1; i >= startX; --i) {                    result.push_back(matrix.at(endY).at(i));                }            }                        // 4. 从下往上            if (endX > startX && endY > startY) {                for (int i = endY - 1; i >= startY + 1; --i) {                    result.push_back(matrix.at(i).at(startX));                }            }        }};