简述二元哈夫曼编码的编码步骤。
参考答案：
1）将q个信源符号按概率递减的方式排列起来；
2）用“0”、“1”码符号分别表示概率最小的两个信源符号，并将这两个概率最小的信源符号合并成一个新的符号，从而得到只包含q-1个符号的新信源，称之为S信源的S1缩减信源；
3）将缩减信源中的符号仍按概率大小以递减次序排列，再将其最后两个概率最小的符号合并成一个符号，并分别用“0”、“1”码符号表示，这样又形成了由q-2个符号构成的缩减信源S2；
4）依次继续下去，直到缩减信源只剩下两个符号为止，将这最后两个符号分别用“0”、“1”码符号表示；5）从最后一级缩减信源开始，向前返回，沿信源缩减方向的反方向取出所编的码元，得出各信源符号所对应的码符号序列，即为对应信源符号的码字。
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| Being positive is very important.So I often__1__my son to be positive.But one day I was caught not __2__what I often tell him to do. My son is 7 years old and he was__3__a show to be put on at his school.He was playing the role of an angel.On the evening before the show,he asked me,"Mom,can we__4__angels?" As usual,I seized (抓住) the__5__to teach him to be positive and I said,"Yes,__6__only those who are perfect,and think and talk positively can." He asked,"You must have seen them then?" I was__7__for a few seconds,not knowing what to say.I was touched by his__8__that his mother was a perfect person.He looked into my eyes,__9__a positive answer.I chose to be__10__with him and told him,"__11__.I've not been a good person all the time." I was almost__12__to admit this to him.I thought that his__13__of a perfect mother would now surely be torn into pieces.But he__14__it positively and said,"It's alright.You know to try to be better__15__." I smiled as I replied,"That's__16__.Sometimes,we might make a__17__,but when we do,we must always try to do better." My son's__18__struck me right in my heart and are always with me.I__19__a good lesson that day "to always try to be better"．This will always__20__me in all situations where I'll need to be positive. | |||
| ( )1. A.paid ( )2. A.saying ( )3. A.going through ( )4. A.describe ( )5. A.feeling ( )6. A.but ( )7. A.pleased ( )8. A.thought ( )9. A.making ( )10. A.wrong ( )11. A.N o ( )12. A.glad ( )13. A.description ( )14. A.finished ( )15. A.in the future ( )16. A.right ( )17. A.plan ( )18. A.words ( )19. A.taught ( )20. A.hurt | B. refuse B. sharing B. preparing for B. draw B. attitude B. so B. interested B. behavior B. expecting B. angry B. Sure B. surprised B. speech B. took B. again and again B. fine B. decision B. performances B. learnt B. protect | C. worry C. doing C. turning to C. invite C. chance C. because C. excited C. dream C. trying C. strict C. OK C. relaxed C. picture C. caught C. from now on C. impossible C. difference C. joy C. organized C. help | D. encourage D. explaining D. looking for D. see D. method D. if D. quiet D. story D. choosing D. honest D. Great D. embarrassed D. idea D. changed D. at times D. unnecessary D. mistake D. progress D. created D. find |