class Solution {

public:

vector<int> spiralOrder(vector<vector<int>>& matrix) {

vector<int> res;

if (matrix.empty() || matrix[0].empty())

return res;

int m = matrix.size();

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

int rowBegin = 0;

int rowEnd = m - 1;

int colBegin = 0;

int colEnd = n - 1;

while (rowBegin <= rowEnd && colBegin <= colEnd)

{

for (int i = colBegin; i <= colEnd; i++)

res.push_back(matrix[rowBegin][i]);

rowBegin++;

if (rowBegin > rowEnd)

break;

for (int i = rowBegin; i <= rowEnd; i++)

res.push_back(matrix[i][colEnd]);

colEnd--;

if (colBegin > colEnd)

break;

for (int i = colEnd; i >= colBegin; i--)

res.push_back(matrix[rowEnd][i]);

rowEnd--;

if (rowBegin > rowEnd)

break;

for (int i = rowEnd; i >= rowBegin && rowBegin <= rowEnd; i--)

res.push_back(matrix[i][colBegin]);

colBegin++;

}

return res;

}

};