螺旋矩阵

给定一个m x n大小的矩阵（m行，n列），按螺旋的顺序返回矩阵中的所有元素。

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int> > &matrix) {
        vector<int> res;
        if(matrix.empty()){
            return res;
        }
        int row = matrix.size();
        int colum = matrix[0].size();
        int up = 0, down = row - 1;
        int left = 0, right = colum - 1;
        // 注意while、for 循环条件要时刻保持
        while(right >= left && down >= up){  	
            for(int i = left; i <= right && up <= down; i++){
                res.push_back(matrix[up][i]);
            }
            up++;
            for(int i = up; i <= down && left <= right; i++){
                res.push_back(matrix[i][right]);
            }
            right--;
            for(int i = right; i >= left && up <= down; i--){
                res.push_back(matrix[down][i]);
            }
            down--;
            for(int i = down; i >= up && left <= right; i--){
                res.push_back(matrix[i][left]);
            }
            left++;
        }
        return res;
    }
};