剑指Offer(19)______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，例如，如果输入如下矩阵： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 则依次打印出数字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.

class Solution {public:    vector<int> printMatrix(vector<vector<int> > matrix) {         vector<int>ans;        if (matrix.size() == 0)return ans;         int left, right, up, down,num;        left = 0, right = matrix[0].size() - 1;        up = 0, down = matrix.size() - 1;        num = matrix.size()*matrix[0].size();        while (ans.size() < num) {            for (int i = left; i <= right; i++)ans.push_back(matrix[up][i]);            up++;            if (up > down)continue;            for (int i = up; i <= down; i++)ans.push_back(matrix[i][right]);            right--;            if (right < left)continue;            for (int i = right; i >= left; i--)ans.push_back(matrix[down][i]);            down--;            for (int i = down; i >= up; i--)ans.push_back(matrix[i][left]);            left++;        }        return ans;    }};