Spiral Matrix

class Solution(object):
    def spiralOrder(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: List[int]
        """
        output = []
        if len(matrix)==0:
            return []
        row_end = len(matrix)-1
        col_end = len(matrix[0])-1
        row_begin, col_begin = 0, 0
        while (row_begin<=row_end) and (col_begin<=col_end):
            for i in range(col_begin, col_end+1):
                output.append(matrix[row_begin][i])
            row_begin += 1
            for i in range(row_begin, row_end+1):
                output.append(matrix[i][col_end])
            col_end -= 1
            if row_begin<=row_end:
                for i in range(col_end, col_begin-1, -1):
                    output.append(matrix[row_end][i])
                row_end -= 1
            if col_begin<=col_end:
                for i in range(row_end, row_begin-1, -1):
                    output.append(matrix[i][col_begin])
                col_begin += 1
                
        return output