题解 | #顺时针打印矩阵#

注意边界，vector类型的vetctor时，即使塞入空的vector实例size()也不为零

#include <vector>
class Solution {
  public:
    int step[4][2] = {
        0, 1,
        1, 0,
        0, -1,
        -1, 0
    };

    vector<int> printMatrix(vector<vector<int> > matrix) {

        int n = matrix.size();
        int m = matrix[0].size();
        if(!n || !m) return {};
        vector<int> ret;
        int i, j, l, r, t, d;
        i = j = l = t = 0;
        r = m - 1;
        d = n - 1;
        ret.push_back(matrix[0][0]);
        while (ret.size() != n * m) {
            for (auto& k : step) {
                while (ret.size() != n * m) {
                    int x = i + k[0];
                    int y = j + k[1];
                    if (x > d) {
                        r--;
                        break;
                    } else if (x < t) {
                        l++;
                        break;
                    }
                    if (y > r) {
                        t++;
                        break;
                    } else if (y < l) {
                        d--;
                        break;
                    }
                    i = x, j = y;
                    ret.push_back(matrix[i][j]);
                }
            }
        }
        return ret;
    }
};