剑指offer-19-顺时针打印矩阵

# -*- coding:utf-8 -*-
class Solution:
    # matrix类型为二维列表，需要返回列表
    def printMatrix(self, matrix):
        # write code here
        if matrix==None:
            return None
        ##找到四个边
        low=0
        height=len(matrix)-1
        left=0
        right=len(matrix[0])-1
        result=[]
        while low<=height and left<=right:
            for i in range(left,right+1):
                result.append(matrix[low][i])
            for j in range(low+1,height+1):
                result.append(matrix[j][right])
            if low<height: ##防止重复操作
                for k in range(right-1,left-1,-1):
                    result.append(matrix[height][k])
            if left<right:  ##防止重复操作
                for l in range(height-1,low,-1):
                    result.append(matrix[l][left])
            ##缩小矩阵
            low+=1
            height-=1
            left+=1
            right-=1
        return result