class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {

        vector<int>ans;
        if( matrix.empty() ) return ans;

        int n = (int)matrix.size();
        int m = (int)matrix[0].size();

        int rowStart = 0;
        int rowEnd = n-1;

        int colStart = 0;
        int colEnd = m-1;

        while( rowStart <= rowEnd &&  colStart <= colEnd )
        {
            // go left to right

            for( int i=colStart; i<= colEnd; i++ )
            {
                ans.push_back(matrix[rowStart][i]);

            }
            rowStart++;

            // go top to down
              for( int i=rowStart; i<= rowEnd; i++ )
            {
                ans.push_back(matrix[i][colEnd]);

            }
            colEnd--;

            // go right to left;
            if(rowStart <= rowEnd)
              for( int i=colEnd; i>=colStart; i-- )
            {
                ans.push_back(matrix[rowEnd][i]);

            }
            rowEnd--;

            // go down to top
            if( colEnd >= colStart )
              for( int i=rowEnd; i>= rowStart; i-- )
            {
                ans.push_back(matrix[i][colStart]);

            }
            colStart++;
        }

        return ans;

    }
};