[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].

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
                vector<int>result;
                int m = matrix.size();
                if(m < 1)return result;
                int n = matrix[0].size();
                if(n < 1)return result;
                int level = (min(m,n)+1)/2;
                for(int l = 0;l < level;l++){
                    //top
                    for(int j = l;j < n-l;j++)
                        result.push_back(matrix[l][j]);
                    //right
                    for(int i = l+1;i < m-1-l;i++)
                        result.push_back(matrix[i][n-1-l]);
                        
                    //bottom
                    for(int j = n-1-l;j >= l && (m-l-1)>l;j--) //top != bottom
                        result.push_back(matrix[m-1-l][j]);
                        
                    //left
                    for(int i = m-2-l;i > l && l < (n-1-l);i--) // left != right
                        result.push_back(matrix[i][l]);
                }
                return result;
    }
};