对读入的某个文本文件input.txt中，拆出英文单词，输出一个按字典顺序排列的单词表，结果输出在文本文件output.txt中，每个单词一行，并在单词后输出该单词出现的个数，两个字段之间用逗号分隔。约定单词仅由英文字母组成，单词间由非英文字母分隔，相同单词只输出一个，大小写不区分。







例如文本文件input.txt为：







Hello world.



Hello every one.



Let us go.







则输出文本文件output.txt为：



every,1



go,1



hello,2



let,1



one,1



us,1



world,1-To read a text file input.txt, divestment English words, the output of an order of the dictionary word list, the result output in a text file output.txt, one word per line, and the output of the word after word the number appears, the two fields separated by commas. Agreed only by the words in English letters, separated by a non-English letters between words, the same output only one word, case-insensitive.



 



Such as a text file input.txt for:



 



Hello world.



Hello every one.



Let us go.



 



The output text file output.txt for:



every, 1



go, 1



hello, 2



let, 1



one, 1



us, 1



world, 1