1.尋找最長公共前綴
（1）掃描法

          

            
              def subString(strs):
    result=strs[0]
    for i in range(1,len(strs)):
        while (strs[i].startswith(result)==False):
            result=result[0:len(result)-1]
            if len(result)==0:
                return "無公共前綴"
    return result
if __name__=='__main__':
    result=subString(['abc','a','an'])
    print result
            
          

            ?