面试题29. 顺时针打印矩阵

输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字。

示例 1：

输入：matrix = [[1,2,3],[4,5,6],[7,8,9]]
输出：[1,2,3,6,9,8,7,4,5]
示例 2：

输入：matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
输出：[1,2,3,4,8,12,11,10,9,5,6,7]

限制：

0 <= matrix.length <= 100
0 <= matrix[i].length <= 100

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/shun-shi-zhen-da-yin-ju-zhen-lcof

1.vector size()
matrix.size()表示二维矩阵有几行。
matrix[0].size()表示二维矩阵有几列。

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        vector <int> ret;
        if (matrix.empty()) return ret;

        int up = 0, down = matrix.size() - 1;
        int left = 0, right = matrix[0].size() - 1;

        while (1){
            for (int i = left; i <= right; i++){
                ret.push_back(matrix[up][i]);
            }
            if (++up > down) break;

            for (int i = up; i <= down; i++){
                ret.push_back(matrix[i][right]);
            }
            if (--right < left) break;

            for (int i = right; i >= left; i--){
                ret.push_back(matrix[down][i]);
            }
            if (--down < up) break;

            for (int i = down; i>= up; i--){
                ret.push_back(matrix[i][left]);
            }
            if (++left > right) break;
        }

        return ret;
        

    }
};