[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 == 0)  return result;
        int n = matrix[0].size();
        int col_beg = 0, col_end = n-1;
        int row_beg = 0, row_end = m-1;
        while(1)
        {
            for(int col = col_beg; col <= col_end; ++col)
                result.push_back(matrix[row_beg][col]);
            if(++row_beg > row_end)   break;
            
            for(int row = row_beg; row <= row_end; ++row)
                result.push_back(matrix[row][col_end]);
            if(--col_end < col_beg)   break;
            
            for(int col = col_end; col >= col_beg; --col)
                result.push_back(matrix[row_end][col]);
            if(--row_end < row_beg)   break;
            
            for(int row = row_end; row >= row_beg; --row)
                result.push_back(matrix[row][col_beg]);
            if(++col_beg > col_end)   break;
        }
        return result;
    }
};