学步园

Given a matrix of m x n elements
(m rows, n columns),
return all elements of the matrix in spiral order.

For example,

Given the following matrix:

[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]

You should return [1,2,3,6,9,8,7,4,5].

进行剥皮操作，先从左到右，再从上到下，再从右到左，最后从下到上。回到原点。

然后开始剥取下一层。

在leetcode上实际执行时间为2ms。

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int> > &matrix) {
        vector<int> result;
        if (matrix.empty() || matrix[0].empty()) return result;

        int iMin = 0, iMax = matrix.size()-1;
        int jMin = 0, jMax = matrix[0].size() - 1;
        while (jMin < jMax && iMin < iMax) {
                int i = jMin, j = jMin;

                while (j<jMax) result.push_back(matrix[i][j++]);
                while (i<iMax) result.push_back(matrix[i++][j]);
                while (j>jMin) result.push_back(matrix[i][j--]);
                while (i>iMin) result.push_back(matrix[i--][j]);

                jMin++;
                jMax--;
                iMin++;
                iMax--;
        }

        if (iMin == iMax && jMin <= jMax)
                while (jMin <= jMax) result.push_back(matrix[iMin][jMin++]);
        else if (jMin == jMax && iMin < iMax)
                while (iMin <= iMax) result.push_back(matrix[iMin++][jMin]);

        return result;
    }
};