使用string类和STL相关容器统计输入文本中所有单词出现的次数。要求：（1）单词统计不分大小写，如Cambridge和CAMBRIDGE是同一单词；（2）标点符号“,. !?”需要过滤；（3）输出结果按照字母大小从小到大排列且输出单词必须是小写，如Cambridge应转化为cambridge后输出。-Use string class and STL the relevant container Statistics input text, the number of all the words appear. Requirements: (1) the word statistics are not case-sensitive, such as the the Cambridge and CAMBRIDGE same word　(2) punctuation " . !?"　Needs to be filtered　(3) the output according to the letter size from small to large arrangement of the output word must be lowercase, such as Cambridge should be translated into cambridge after output.