LeetCode: Spiral Matrix

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] .
境界に注意する.

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int> > &matrix) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> result;
        int m = matrix.size();
        if (m == 0) return result;
        int n = matrix[0].size();
        if (n == 0) return result;
        
        int min = (m < n ? m : n);
        int layer = min / 2;
        for (int i = 0; i < layer; ++i)
        {
            for (int j = i; j < n-1-i; ++j)
            {
                result.push_back(matrix[i][j]);
            }
            for (int j = i; j < m-1-i; ++j)
            {
                result.push_back(matrix[j][n-1-i]);
            }
            for (int j = n-1-i; j > i; --j)
            {
                result.push_back(matrix[m-1-i][j]);
            }
            for (int j = m-1-i; j > i; --j)
            {
                result.push_back(matrix[j][i]);
            }
        }
        if (min % 2 == 1)
        {
            if (m > n)
            {
                for (int i = layer; i <= m-1-layer; ++i)
                    result.push_back(matrix[i][n/2]);
            }
            else
            {
                for (int i = layer; i <= n-1-layer; ++i)
                    result.push_back(matrix[m/2][i]);
            }
        }
    }
};